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DESCRIPTIVE MINERALOGY 



MINERALOGY 



BY 

WILLIAM SHIRLEY BAYLEY, PH.D. 

PBOFXBSOR OP GEOLOGY. T7NTVTBBSITY OF ILLINOIS 
AUTHOR OF "BLEMENTABY CBYSTAI,IX)OKAPHX " 




"WITH TWO HTCnSTDKED AND SIXTY-EIGHT ILLUSTRATIONS 



D. APPLETON AND COMPANY 

NEW YORK AND LONDON 

1917 



COPYRIGHT, 1917, BY 
D APPLETON AND COMPANY 



TO 
MY HELPER 

MY WIFE 

THIS BOOK IS 
DEDICATED 



PREFACE 

THE following pages are presented with the purpose of affording 
students a comprehensive view of modern mineralogy rather than a 
detailed knowledge of many minerals The -minerals selected for 
description are not necessarily those that are most common nor those 
that occur in greatest quantity The list includes those that are of 
scientific interest or of economic importance, and, in addition, those 
that illustrate some principle employed in the classification of minerals. 
The volume is not a reference book. It is offered solely as a textbook 
It does not pretend to furnish a complete discussion of the mineral 
kingdom, nor a means of determining the nature of any mineral that 
may be met with The chapters devoted to the processes of deter- 
minative mineralogy are brief , and the familiar " key to the determina- 
tion of species " is omitted In place of the latter is a simple guide 
to the descriptions of minerals to be found in the body of the text. 
For more complete determinative tables the reader is referred to one 
of the many good books that are devoted entirely to this phase of the 
subject. In the descriptions of the characteristic crystals of minerals 
both the Naumann and the Miller systems of notation are employed, 
the former because of its almost general use in the more important refer- 
ence books and the latter because of its almost universal use in modern 
crystallography investigations The student must be familiar with 
both notations It is thought that this familiarity can be best acquired 
by employing the two notations side by side 

In preparing the descriptive matter the author has made extensive 
use of Hintze's Handbuch der Mvrwralogie. The figures illustrating 
crystal forms are taken from many sources. A few illustrations have 

VII 



viii PREFACE 

been made especially for this volume. Figures copied to illustrate 
special features are accredited to their authors. The statistics are 
mainly from the Mineral Resources of the Umted States They are 
given for the year 1912 because this was a more nearly normal year in 
trade than any that has followed 

The author is under obligation to the McGraw-Hill Book Company 
for permission to reproduce a number of illustrations originally published 
in his Elements of Crystallography, and also for the use of the original 
engravings m making the plates for Figures n, 33, 71, 90, no, 114, 115, 
118, 160, 191, 194, 224, 240, and 248. 

W. S. BAYLEY. 



CONTENTS 
PART I 

GENERAL CHEMICAL MINERALOGY 

CHAPTER PAGE 

I THE COMPOSITION AND CLASSIFICATION OF MINERALS i 

II THE FORMATION OF MINERALS AND THEIR ALTERATIONS 17 

i 

PART II 
DESCRIPTIVE MINERALOGY 

III INTRODUCTION THE ELEMENTS 36 

IV THE SULPHIDES, TELLURIDES, SELENIDES, ARSENIDES, AND 

ANTIMONIDES 68 

V THE SULPHO-SALTS AND SULPHO-FERRITES. Il6 

VI THE CHLORIDES, BROMIDES, IODIDES, AND FLUORIDES. 134 

VII THE OXIDES 146 

VIII THE HYDROXIDES 179 

IX. THE ALUMINATES, FERRITES, CHROMITES AND MANGANTTES 195 

X. THE NITRATES AND BORATES 205 

XI THE CARBONATES 212 

XII THE SULPHATES 236 

XIH THE CHROMATES, TUNGSTATES AND MOLYBDATES 253 

XIV THE PHOSPHATES, ARSENATES AND VANADATES. 261 

XV THE COLUMBATES, TANTALATES AND URANATES 293 

XVI THE SILICATES THE ANHYDROUS ORTHOSELICATES . 300 

XVII THE SILICATES THE ANHYDROUS METASILICATES . 359 

XVIII THE SILICATES THE ANHYDROUS TRIMETASILICATES. . 408 

XIX THE SILICATES THE ANHYDROUS POLYSILICATES . 426 

XX THE SILICATES THE HYDRATED SILICATES . 441 

XXI THE SILICATES THE TITANATES AND TTTANOSILICATES. .. 461 

PART III 
DETERMINATIVE MINERALOGY 

XXII GENERAL PRINCIPLES OF BLOWPIPE ANALYSIS. 467 
XXIH CHARACTERISTIC REACTIONS OP THE MORE IMPORTANT ELEMENTS 

AND Aero RADICALS, , . 483 
ix 



CONTENTS 



APPENDICES 

CHAPTER PAGE 

I GUIDE TO THE DESCRIPTIONS or MINERALS 495 
II LIST or THE MORE IMPORTANT MINER AIS ARRANGED ACCORD- 
ING TO THEIR PRINCIPAL CoNSTrrui'Nib 515 

III LIST OP MINERALS ARRANGED ACCORDING TO THEIR CRYS- 

TALLIZATION 521 

IV LIST OF REFERENCE BOOKS 527 
INDEX 529 



LIST OF ILLUSTRATIONS 

FIGURE PAGE 

1 Sodium fluosihcate crystals ... 14 

2 Potassium fluosihcate crystals 14 

3 Cross-section of symmetrical vein 21 

4 Cross-section of vein in green porphyry 24 

5 Dionte dike cutting granite gneiss 26 

6 Vein in Griffith mine 27 

7 Vein forming original ore-body, Butte, Mont 27 

8 Druse of Smithsonite 28 

9 Geodes containing calcite 29 

10 Alteration of ohvine into serpentine 31 

11 Etch figures in cubic face of diamond 38 

12 Crystal of diamond with rounded edges and faces 38 

13 Octahedron of diamond 38 

14 Principal "cuts" of diamonds 42 

15 Premier diamond mines m South Africa 43 

1 6 The Cullman diamond 43 

17 Gems cut from Culhnan diamond . 44 

1 8 The Tiffany diamond 44 

19 Sulphur crystals 47 

20 Distorted crystal of sulphur. ... 47 

21 Copper crystal 53 

22 Crystal of copper from ELeweenaw Point 53 

23 Plate of silver from Comagas Mine, Cobalt 57 
24. Octahedral skeleton crystal of gold with etched faces 58 

25 Iron meteonte 65 

26 Widmanstatten figures on etched surface of meteonte 66 

27 Realgar crystal . . 70 

28 Stibrute crystal 72 

29 Galena crystal 81 

30 Galena crystals . 82 

31 Chalcocite crystal 85 

32 Complex chalcocite twin 85 

33 Tetrahedral crystal of sphalerite 88 
34. Sphalerite crystal , 88 

35 Sphalerite octahedron . 88 

36 Greenockite crystal . . 91 

37 Pyrrhotite crystal. 92 



xu LIST OF ILLUSTRATIONS 

FIGURE PAGE 

38 Cinnabar crystals 98 

39 Group of pyrite crystals in which the cube predominates 102 

40 Pyrite crystals on which 0(111) predominates 102 

41 Pyrite crystal 102 

42 Group of pyrite crystals 103 

43 Pyrite mterpenetration twin 103 

44 Marcasite crystal no 

45 Marcasite crystal with forms as indicated m Fig 44 no 

46 Twin of marcasite no 

47 Spearhead group of marcasite no 

48 Arsenopynte crystals 112 

49 Crystal of pyrargyrite ng 

50 Crystal of proustite 119 

51 Bournonite crystal 121 

52 Bournonite fourlmg twinned 121 

53 Enargite crystal 123 

54 Stephanite crystal 125 

55 Tetrahednte crystal I2 8 

56 Chalcopynte crystal I3I 

57 Chalcopynte 131 

58 Chalcopynte twin 13! 

59 Hopper-shaped cube of halite , 135 

60 Group of fluonte crystals from Weardale Co 139 

6 1 Crystal of fluonte !4 O 

62 Interpenetration cubes of fluonte, twin- 140 

63 Photographs of snow crystals 147 

64 Zmcite crystal !^ 

65 Hematite crystals j^ 

66 Corundum crystal j^ 

67 Corundum crystal ^5 

68 Corundum crystal I ^ 

69 Quartz crystal exhibiting rhombohedral symmetry 159 

70 Ideal (A) and distorted (B) quartz crystals . 159 

71 Etch figures on two quartz crystals of the same form , 160 

72 Group of quartz crystals , jgo 

73 Tapenng quartz crystal X 5 X 

74 Quartz crystal , ufa 

75 Supplementary twins of quartz. , ,162 

76 Quartz twinned I0 * 3 

77 Cassitente crystal , . . 169 

78 Cassitente crystal , ^ 

79 Cassitente twinned j$g 

80 Rutile crystals 172 
81. Rutile eightluig twinned , . , 2 



LIST OP ILLUSTRATIONS 

FIGURE 

82 Rutile twinned . . 172 

83 Rutile cycbc sixling twinned j^ 

84 Rutile twinned ^. 

85 Anatase crystal I77 

86 Anatase crystal I77 

87 Brookite crystals I7 3 

88 Brucite crystal f !3 2 

89 Limonite stalactites in Silverbow mine. . , 184 

90 Botryoidal hmorute . . jg^ 

91 Pisohtic bauxite from near Rock Run . 187 

92 Diaspore crystals , I9O 

93 Mangamte crystal . . I92 

94 Group of prismatic mangamte crystals 192 

95 Mangamte crystal twinned . . 193 

96 Spinel twin . . ig5 

97 Spinel crystal . 196 

98 Magnetite crystal . 198 

99 Chrysoberyl crystal 203 

100 Chrysoberyl twinned . . 203 

101 Chrysoberyl pseudohexagonal sixling . 203 

102 Hausmanmte . . 204 
103. Borax crystal . . 207 

104 Colemamte crystals .... 209 

105 Boracite crystal 211 

106 Calcite crystal . 214 

107 Calcite crystals 214 

108 Calcite crystals 214 

109 Calcite . ....... 214 

no Prismatic crystals of calcite 215 

in Calcite . 215 

112 Calcite twin and polysynthetic trilling. 215 

113 Calcite 216 

114 Artificial twin of calcite , 216 

115 Thin section of marble viewed by polarized fight. . 216 

1 16. Aragonite crystal 224 

117. Aragonite twin 224 

118 Tnlhng of aragomte 224 

119 Withente twinned . 226 

120. Cerussite crystal . . 227 

121. Cerussite tnllmg twinned . , 227 

122. Cerussite trilling twinned 227 

123. Radiate groups of cerussite on galena . . -228 

124. Dolomite crystal. . - 229 

125. Group of dolomite crystals. . 230 



X1V LIST OF ILLUSTRATIONS 

FIGURE PAGE 

126 Malachite crystal .232 

127 Azurite crystals 233 

128 Trona crystal 235 

129 Gayhissite crystal 235 

130 Glauberite crystal 237 

131 Thenardite crystal 237 

132 Thenardite twinned 237 

133. Bante crystals 239 

134. Bante crystals 240 

135. Celestite crystals 241 
136 Anglesite crystal 243 
137. Anglesite crystal 243 
138 Anglesite crystal 243 

139. Gypsum crystals 247 

140. Gypsum twinned 247 

141. Gypsum twinned 248 

142. Epsomite crystal 250 

143. Hanksite crystal 252 

144. Crocoite crystals 253 

145. Scheelite crystal . 255 

146. Scheelite crystal 255 

147 Wulfemte crystal 257 

148 Wulfemte crystal , . 257 

149 Wolframite crystal 250 
150. Monazite crystal , 264 

151 Xenotime -crystals 265 

152 Apatite crystal , 267 

153 Apatite crystal . . 267 
154- Vanadimte crystal . 262 
155. Skeleton crystal of vanadmite . .272 

156 Amblygomte crystal , 2 ^ 

157. Lazulite crystals , . , . 2 ^6 

158 Olivemte crystal. , 27^ 

159 Skorodite crystal 286 

160 Radiate wavelhte on a rock surface . , , 287 
161. Columbite crystals . , ^ 

162 Samarskite crystals . . . , > . 297 

163 Olivme crystals , , 3P3 

164 Willemite crystal , , 3O7 

165 Phenacite crystal , 3O g 
166. Garnet crystal (natural size) . 3IO 

167 Garnet crystals ,, , , .310 

168 Garnet crystal , 31O 

16^) Nephehue crystal, , I 



LIST OF ILLUSTRATIONS 



X v 

PAGE 



. , 

170 Zircon crystals ....... .317 

171 Zircon twinned . 

172 Thorite crystal 3I p 

173 Andalusite crystals , 2O 

174 Topaz crystals 32 - 

175 Topaz crystal 323 

176 Topaz crystal ,24 

177 Danbunte crystal 325 

178 Zoisite crystal ^ 

179 Epidote crystal ^ 2 g 
1 80 Epidote crystals 328 

181 Chondrodite crystal 333 

182 Datolite crystal 334 

183 Staurolite crystal 337 

184 Staurolite crystal twinned 337 

185 Staurolite crystal twinned 33-7 
1 86 Sodalite mterpenetration twin of t\vo dodecahedrons 340 
187 Prehmte crystal - 344 
1 88. Axinite crystal 346 

189 Axmite crystal . 346 

190 Dioptase crystal 347 

191 Percussion figure 348 

192. Biotite crystal 349 

193. Biotite twinned about a plane . 349 

194 Etch figures 356 

195 Muscovite crystal 356 

196 Beryl crystals .. 360 

197 Beryl crystals . . 360 
198. Cross-section of pyroxene * , 363 

199 Enstatite crystal. . 366 

200 Wollastomte crystal * . 368 

201. Augite crystal . . 37* 

202. Augite twinned . 371 

203 Interpenetration twin of augite . 371 

204 Diopside crystals , . 372 
205, Hedenbergite crystal 373 
206* Acnute crystal , 3 76 
207. Spodumene crystal. . . 379 
208 Rhodonite crystals 3&> 
209;. Ampibole crystals * 3^4 
210. Kyanite crystals 394 
211 Bladed kyanite crystals in a micaceous quartz schist 395 

212. Calarmne crystals , 30 

213. Orthoclase crystals . . . , , ...... 410 



xvi LIST OP ILLUSTRATIONS 

FIGURE PAGE 

214 Orthoclase crystals 410 

215 Carlsbad mterpenetration twins of orthoclasc 410 

216 Contact twin of orthoclase according to the Carlsbad law 4IO 

217 Baveno twins of orthoclase 411 

218 Manebach twin of orthoclase 411 

219 Section of mirocline viewed between crossed nicols 4x4 

220 Adulana crystal 414 

221 Albite crystals 419 

222 Albite twinned 419 

223 Albite twinned 419 

224 Twinning stnations on cleavage piece of ohgoclasc 420 

225 Albite twins with the crystal axis 420 

226 Position of "rhombic sections" in albite . 420 

227 Diagram of crystal of tnclimc feldspar f 420 

228 Potash-oligoclase crystal 422 

229 Scapohte crystals 424 

230 Chntonite twinned according; to the mica law 427 

231 Cknochlore crystal 430 

232 Clmochlore twinned according to mica law 430 

233 Chnochlore with same forms as m Fig 232 430 

234 Clmochlore tnllmg twinned according to mica law 430 

235 Pennimte crystal 430 

236 Pennimte crystal twinned 430 

237 Vesuviamte crystals . 433 
238. Tourmaline crystals 436 

239 Tourmaline crystals 436 

240 Cooling crystal of tourmaline 436 

241 Cordiente crystal . . , 439 

242 Apophylhte crystals 444 

243 Heulandite crystal , , 447 

244 Heulandite, var beaumontJte . . 447 

245 Philhpsite mterpenetration twin , , 448 

246 Phillipsite , 448 

247 Harmotome fourling twinned like pmllipsite . 449 

248 Sheaf-like aggregates of stilbite , . 450 

249 Laumontite crystal 452 

250 Divergent groups of scolecite crystals 453 

251 Scoleate crystal , 453 

252 Natrohte crystals , , . 434 
253. Thomsomte crystal . , ... 456 

254 Chabazite crystal t 4^ 7 

255 Chabazite mterpenetration twin . . 457 
256. Phacohte with same form as in Fig 254 . 457 
257 Analate crystal , t 4 



LIST OF ILLUSTRATIONS 



xvi 



FIGURE PAGE 

258 Analcite crystal . , , . , 4 - 9 

259 Ilmemte crystal 4 6 3 

260 Titanite crystal 4 g 4 

261 Titanite crystal 4 ^ 4 

262 Titanite crystal 4 5 4 

263 Simple blowpipes 4 gg 

264 Bellows for use with blowpipe 468 

265 Candle flame showing three mantles 47 o 

266 Reducing flame 4 y Z 

267 Oxidizing flame 4 ^ r 
268. Props and position of charcoal 4 ^ 5 



DESCRIPTIVE MINERALOGY 



PART I 
GENERAL CHEMICAL MINERALOGY 



CHAPTER I 

THE COMPOSITION AND CLASSIFICATION OF MINERALS 

Definition of Mineral. A mineral is a definite inorganic, chem- 
ical compound that occurs as a part of the earth's crust. It possesses 
characters which are functions of its composition and its structure. 
Most minerals are crystallized, but a few have been found only in an 
amorphous, colloidal condition. These are regarded as gels, or solid 
colloids. 

The most essential feature of a mineral is its chemical composition, 
since upon this are believed to be dependent all its other properties. 

Chemical Substances Occurring as Minerals. The chemical 
substances found native as minerals may be classed as elements and 
compounds The latter comprise chlorides, fluorides, sulphides, oxides, 
hydroxides, the salts of carbonic, sulphuric, phosphorus, arsenic, anti- 
mony and silicic acids, a large series of complicated compounds known 
as the sulpho-salts, a few derivatives of certain metallic acids the 
aluminates and the ferrites besides other salts of rarer occurrence, 
some simple and others exceedingly complicated, and possibly many 
solid solutions of gels or of a gel and a crystalloid. In some of these 
classes all the compounds are anhydrous. In others, some groups are 
anhydrous while the members of other groups contain one or more 
molecules of water of crystallization. 

The sulphides, chlorides and fluorides are derivatives of EfeS, HC1, 
and ifeFs, respectively. They may be regarded as having been pro- 
duced from these compounds by the replacement of the hydrogen by 
metals. Illustrations: CuaS, CuS, NaCl, CaF2. 



2 GENERAL CHEMICAL MINERALOGY 

The hydroxides and the oxides may be looked upon as derivatives of 
water, the hydroxides through the replacement of one atom of hydrogen 
by a metal, and the oxides through the replacement of both hydrogen 

/OH 

atoms The mineral, bructte, according to this view is Mg/ , 

H(OH) X)H 

derived from rr^rr\ by replacement of two hydrogen atoms in two 
H(OH) 

molecules of water by one atom of Mg Cuprite is >0, and tenonte 

Cu/ 

CuO, the former derived by replacement of each atom of hydrogen m 
one molecule of water by an atom of Cu, and the latter by replacement 
of the two hydrogens by a single Cu 

The salts of carbonic acid (H 2 COs) are the carbonates, those of sul- 
phuric acid (HaSO*) the sulphates, those of orthophosphoric acid 
(HsP04) the phosphates, those of orthoarsemc acid (HsAsO^ the arsen- 
ates, those of orthoantimomc acid (HaSbO-i) the antimonates and those 
of the silicic acids, the silicates There are, in addition, a few arsenites 
and antimonites that are salts of arsemous (HsAsOa) and antimonous 
(H 3 Sb0 3 ) acids 

The principal silicic acids whose salts occur as minerals are normal 
silicic acid (H4Si04), metasihcic acid (HaSiOj), and tribilicic acid 
(HiSiaOs) The metasihcic and the tribihcic acids may be regarded 
as normal silicic acid from which water has been abstracted, m the same 
way that pyrosulphuric acid is ordinary sulphuric acid less H 2 0, thus: 
2H2SO*- H 2 H 2 S 2 7 

(HO)4Si-H 2 0=H 2 Si03, metasihcic acid 
3(HO)4Si-4H20=H 4 Si30, tnsihcic acid. 

Faydite is Fe 2 Si04, wollastonite, CaSiOs, and ortkoctase, KAlSisOs- 
The alummates and ferntes may be regarded as salts of the hypothet- 
ical acids AIO(OH) and FeO(OH), both of which exist as minerals, 
the first under the name dtaspore and the second under the name 

yO A10 

goethite. Spinel is the magnesium aluminate, Mg<f .(MgAfeO*), 

\0-A10 
and magnofernte the corresponding ferrate MgFe 2 04. The very com- 

X) FeO 
mon mineral magnetite is the iron ferrate Fe<; , or FesO*, In 

X>-FeO 

this compound the iron is partly in the ferrous and partly in the ferric 
state. 



COMPOSITION AND CLASSIFICATION 3 

There are other minerals that differ from those of the classes above 
mentioned in containing more or less water of crystallization These 
are usually separated from those m which there is no water of crystal- 
lization under the name of hydrous salts 

Besides the classes of minerals considered there are others which 
appear to be double salts, m which two substances that may exist 
independently occur combined to form a third substance with prop- 
erties different from those of its components Cryolite, sNaF-AlFa 
or NasAlFe, is an example The sulpho-salts furnish many other 
examples 

Further, a large number of minerals are apparently isomorphous 
mixtures of several compounds These are homogeneous mixtures 
of two or more substances that crystallize with the same sym- 
metry, and, consequently, that may crystallize together Their 
physical properties are continuous functions of their chemical com- 
positions. Other minerals are apparently solid solutions in one an- 
other of simple crystallizable salts, of gels, of gels and salts, and of 
gels and adsorbed substances Among these are some of the commoner 
silicates. 

Determination of Mineral Composition. Since the properties 
of minerals are functions of their chemical compositions, it is important 
that their compositions be known as accurately as possible. It is 
necessary in the first place that pure material may be secured for study 
Pure material is most easily secured by making use of the differences 
in density exhibited by different compounds The mineral to be studied 
is pounded to a powder, sifted through a bolting doth sieve and shaken 
up with one of the heavy solutions employed in determining specific 
gravities. When the solution is brought to the same density as that 
of the mineral under investigation all material of a higher specific gravity 
will sink. The material with a density lower than that of the solu- 
tion will rise to the surface Material with a specific gravity identical 
with that of the solution will be suspended in it If the mixing is done 
in a separating funnel of the proper type, the materials may be drawn 
off into beakers in the order of their densities, and thus the pure mineral 
may be separated from the impurities that were originally incorporated 
with it. After the purity of the substance is assured by examination 
under the microscope, it is ready for analysis 

The composition of the purified material is determined by the 
ordinary methods of chemistry known as analysis and synthesis. 

In analysis the compound is broken into its constituent parts and 
these are weighed, or it is decomposed and its constituents are trans- 



4 GENERAL CHEMICAL MINERALOGY 

formed into known compounds which are weighed From the weights 
thus obtained the proportions of the components m the original sub- 
stance may be easily calculated if the weight of the original substance 
be known 

In synthesis the compound is built up from known elements or 
compounds 

If the mineral caicite (CaCOs) is decomposed by heat into lime 
(CaO) and carbonic acid gas (CCte), or if its components are trans- 
formed into the known compounds CaSCU and KaCOj, the process is 
analysis If the known substance CCfe is allowed to act upon the 
known substance CaO and the resulting product is a substance possess- 
ing all the properties of caicite, the process is synthesis. 

Analytical Methods. The analytical methods made use of in 
mineralogy are (i) the ordinary wet methods of chemical analysis, 
(2) the dry methods of blowpipe analysis, in which the mineral is 
treated before the blowpipe without the use of liquid reagents except 
to a very subordinate degree, and (3) microchemical methods, per- 
formed on the stage of a compound microscope. 

Blowpipe and microchemical analyses are made use of principally 
for the identification of minerals By their aid the nature of the atoms 
m a compound may easily be learned, but the proportions in which 
these atoms are combined is determined only with the greatest difficulty. 
The methods are mainly qualitative 

Wet Analysis. For exact determinations of composition the wet 
methods of chemistry are usually employed, since these are the most 
accurate ones They are identical with the methods described in 
manuals of quantitative analysis, and therefore require no detailed 
discussion here They are well illustrated by Prof Tschermak as 
follows. If 734 mg. of the mineral goethite (in which qualitative tests 
show the presence of iron oxide and water) are roasted in a glass tube, 
water is given off This when caught and condensed m a second tube 
containing dry calcium chloride increases the weight of this second 
tube by 75 mg The residue of the mineral left in the first tube now 
weighs about 660 mg An examination of this residue shows it to con- 
sist exclusively of the iron oxide (FejjOs) Since only iron oxide and 
water are present in goethite the sum of these two constituents ought to 
equal the original weight of the mineral before roasting But 660+75 * 
73SJ whereas the original weight was 734 The difference i mg. is| 
due to unavoidable errors of manipulation. As it is very small it may" 
be neglected in our calculations 

The results of the analysis are generally expressed in percentages. 



COMPOSITION AND CLASSIFICATION 5 

which are obtained by dividing the weights of the different constituents 
by the weight of the original substance 

Thus: 660- 734= 89 92 per cent Fe 2 0s 

75"~734= 10 22 per cent EfeO 

Total 100 14 

The usual methods of analysis are, however, more indirect than this, 
the components of the substance to be analyzed being first transformed 
into known compounds and then weighed For instance, common salt 
is known by qualitative tests to contain only Na and CL If 345 mg. 
of the pure salt be dissolved in water and the solution be treated with 
silver nitrate under proper conditions a precipitate of silver chloride 
is formed so long as any sodium chloride remains in the solution. The 
silver chloride is separated from the solution by filtration It contains 
all the chloride present m the 345 mg of salt After drying, its weight 
is determined to be 840 mg The solution from which the silver chloride 
was separated contains all the sodium that was originally present in 
the salt, but now it is in combination with nitric acid It contains 
also any excess of silver nitrate that was added to precipitate the chlorine 

NaCl + AgNOs - AgCl + NaN0 3 

salt reagent precipitate filtrate 

The filtrate is now treated with hydrochloric acid to precipitate 
the excess silver The silver chloride precipitate is removed by filtra- 
tion, leaving a solution containing sodium salts of nitric and hydro- 
chloric acids besides some free acid of each kind. Sulphuric acid is 
now added and the whole solution is evaporated to dryness. The free 
acids are driven off by the heat and the sodium salts are transformed 
into the sulphate, Na2S04 The residue consisting exclusively of NaaSO* 
is now found to weigh 419 mg. 

The 345 mg of salt have yielded 840 mg. of AgCl and 419 mg. of 
NagS04 The silver chloride is known to contain 24 74 per cent of 
chlorine and the sodium sulphate 32 39 per cent of sodium. The 840 
mg of AgCl contain 207.8 mg of chlorine, and the 419 mg of 
contain 135 7 mg. of sodium. Hence 345 mg of salt yield 

207.8 mg. or 60.23 per cent Cl, 
and 135 7 mg. or 3934 per cent Na 

343.5 mg. 99.57 per cent 



6 GENERAL CHEMICAL MINERALOGY 

Records of Analyses. The composition of minerals like that of 
other chemical compounds is determined in percentages of their com- 
ponents and is recorded as parts per 100 by weight. A weighed quantity 
of themmeral is analy/ed, the products of the analysis are weighed and the 
percentage of each constituent present is found by dividing its weight 
by the weight of the original substance, as has already been indicated 

In chemical treatises the results of the analyses are usually recorded 
in percentages of the elements present. In mineralogical works it is 
more common to write the percentage composition in terms of the 
oxides of the elements, partly because the old analyses are recorded in 
this way and partly because certain relations between the mineral 
components can be better exhibited by comparison of the oxides than 
by comparison of the elements present in them. 

The record of the analysis of a magnestte may be given as. 



Mg=2835 per cent, 

Fe= 34 per cent, 

0=14 25 per cent, 

0=5698 per cent, 

Total =99,92 per cent 



or as 



MgO=47 2 5 per cent, 
FeO= 43 per cent, 
C02=S2 24 per cent, 

Total =99 92 per cent. 



Calculation of Formulas. After the determination of the per- 
centage composition of a mineral, the next step is to represent this 
composition by a chemical formula a symbol which indicates the 
relative number of elementary atoms in the mineral's molecule, instead 
of the number of parts of its constituents in 100 parts of its sub- 
stance. 

The construction of a formula from the analytical results is simple 
enough in principle, but in practice it is often made difficult by the 
fact that many apparently pure substances are in reality composed of 
several distinct compounds so intimately mtercrystalhzed that it is 
impossible to separate them In the simplest cases the formula is 
derived directly from the results of the analyses by a mere process of 
division. 

The atomic weights of the chemical elements are the relative weights 
of the smallest quantities that may enter into chemical combination with 
one another, measured in terms of the atomic weight of hydrogen which 
is taken as unity, or of oxygen taken as 16. Thus the atomic weights 
of nitrogen and oxygen are approximately 14 and 16 respectively, i.e., 
the smallest quantities of nitrogen and oxygen that can enter into com- 
bination with each other and with hydrogen are in the ratio of the 



COMPOSITION AND CLASSIFICATION 



TABLE OF ATOMIC WEIGHTS 



Element 


Symbol 


At Weight 


Element Symbol 


At. Weight 


Aluminium 


Al 


27 i 


Molybdenum 


Mo 


96 o 


Antimony 


Sb 


120 2 


Neodymium 


Nd 


144 3 


Argon 


A 


3988 


Neon 


Ne 


20 2 


Arsenic 


As 


74 96 


Nickel 


Ni 


58 68 


Barium 


Ba 


137 37 


Niton 


Nt 


222 4 


Bismuth 


Bi 


208 o 


Nitrogen 


N 


14 oi 


Boron 


B 


II 


Osmium 


Os 


190 9 


Bromine. 


Br 


79 92 


Oxygen 





16 o 


Cadmium 


Cd 


112 40 


Palladium 


Pd 


106 7 


Caesium 


Cs 


132 81 


Phosphorus 


P 


31 04 


Calcium 


Ca 


40 07 


Platinum 


Pt 


195 2 


Carbon 


C 


12 OOS 


Potassium 


K 


39 10 


Cerium 


Ce 


140 25 


Praseodymium 


Pr 


1409 


Chlorine 


Cl 


35 46 


Radium 


Rd 


226 o 


Chromium 


Cr 


52 


Rhodium 


Rh 


102 9 


Cobalt 


Co 


58 97 


Rubidium 


Rb 


85 45 


Columbium 


Cb 


93 5 


Ruthenium 


Ru 


101 7 


Copper. 


Cu 


63 57 


Samanum 


Sa 


1504 


Dysprosium 


Dy 


162 5 


Scandium . 


Sc 


44 i 


Erbium 


Er 


167 7 


Selenium 


Se 


79 2 


Europium 


Eu 


152 o 


Silicon 


Si 


28 3 


Fluorine 


F 


19 o 


Silver 


Ag 


107 88 


Gadolinium 


Gd 


157 3 


Sodium 


Na 


23 o 


Gallium 


Ga 


69 9 


Strontium 


Sr 


8763 


Germanium 


Ge 


72 5 


Sulphur 


S 


32 06 


Glucinum 


Gl 


9 i 


Tantalum 


Ta 


181 5 


Gold.. 


Au 


197 2 


Tellurium 


Te 


127 5 


Helium 


He 


4 oo 


Terbium 


Tb 


159 2 


Holmmm. 


Ho 


163 5 


Thallium 


Tl 


204 o 


Hydrogen 


H 


i 008 


Thorium 


Th 


232 4 


Indium. 


In 


114 8 


Thulium 


Tm 


168 5 


Iodine. . . 


I 


126 92 


Tin 


Sn 


118 7 


Indium. . 


Ir 


193 i 


Titanium 


Ti 


481 


Iron 


Fe 


55 85 


Tungsten 


W 


184 o 


Krypton 


Kr 


82 92 


Uranium 


U 


238 2 


Lanthanum 


La 


139 o 


Vanadium 


V 


51 06 


Lead . 


Pb 


207 20 


Xenon 


Xe 


130 2 


Lithium.... 


U 


6 94 


Ytterbium (Neoytterbium) 


Yb 


173 5 


Lutecium.. 


Lu 


1750 


Yttrium, . 


Y 


88 7 


Magnesium. .. 


Mg 


24 32 


Zinc . 


Zn 


65 37 


Manganese. . 


..Mn 


54 93 


Zirconium 


,Zr 


90 6 




..,,Hg 


200,6 









8 GENERAL CHEMICAL MINERALOGY 

values 14 1 6 : i l The quantities that possess these relative weights 
are known as atoms Often the apparent ratios ot the elements in 
combination are different from the uitios between their atomic weights, 
but this is always due to the fact that one or the other of the elements 
is present in more than its smallest possible quantity, i e , in a greater 
amount than is represented by a single atom For instance, there are 
several compounds of oxygen and nitrogen known, in which the weight 
relations between the two elements may be represented by the follow- 
ing figures 14 : 8, 14 : 16, 14 24, 14 : 32, and 14 : 40 If the 
second of these compounds consists of one atom each of nitrogen and 
oxygen, and these are the smallest quantities of the elements that 
can exist in combination, the several compounds must be made up thus 

14 : 8 14 . 16 14 . 24 14 : 32 14 * 40 

N 2 O NO N 2 3 N0 2 N 2 5 

for N can exist only in quantities that weigh 14, 28, 42 times as much 
as the smallest quantity of hydrogen present in any compound, i e , 
the single atom, and in quantities of 16, 32, 48, etc , times the weight 
of the single hydrogen atom In order that even multiples of 14 and 
1 6 shall exist in the ratios given above, their terms must be multi- 
plied by quantities that will yield the following results. 

28 . 1 6 14 : 16 28 48 14 32 28 : 80 

which are the weights respectively of the numbers of atoms lepresented 
in the above formulas 

If, then, the elements combine in the ratio of their atomic weights, 
or in some multiple of this ratio, the figures obtained by analysis must 
be in one of these ratios, and consequently they furnish the data from 
which the formula of the substance analyzed may be deduced In 
gold chloride, for example, analysis shows the presence of 64 87 per cent 
Au and 35 13 per cent Cl, i e , the gold and the chlorine are united in 

the ratio of 64.87 ; 35 13 or -i-I. The combining ratio of single 

tjj 5 

atoms of gold and of chlorine is, however, 196 7 35 5, or -2Z V i- 

oo 5 
dently in gold chloride the ratio of gold to chlorine is only one-third 

as great as is the ratio between the atomic weights of these elements, 
or the ratio of the chlorine to the gold three times as great. Hence 

1 The atomic weight of hydrogen is more accurately i 008, when that of oxygen 
is taken as 16 



COMPOSITION AND CLASSIFICATION 



9 



there must be three times as much chlorine in gold chloride as would 
be represented by a single atom of chlorine, or there must be three 
atoms of chlorine in the compound, for we cannot imagine a quantity 
of gold present which is equivalent to one-third of an atom of gold 
Gold chloride is therefore AuCls 

We can now prove our conclusion by calculation One atom of 
gold and three atoms of chlorine ought to combine in the ratio of 
1967:1065 (le, 355X3) If our conclusion is correct, and the 
gold chloride analyzed is AuCls, then the quantities of gold and of 
chlorine yielded by the analysis should be in this ratio The figures 
obtained are in the ratio of 64 87 : 35 13 Multiplying both terms of 
this ratio by 3 031 we obtain 196 62 . 106 5, which is approximately 
the ratio expected. 

In practice, the same result as that outlined above is reached by 
dividing the results of analyses by the atomic weights of the various 
elements or groups of elements concerned The quotients represent the 
proportional numbers of the elements or groups present. If the small- 
est quotient is assumed as unity, the ratios existing between this and 
the other quotients indicate the number of atoms or groups of 
atoms represented by the latter. 

Illustrations, 



Gold Chloride Result of Analysis Atomic Weights Quotients 

Au = 64 87 per cent 196 7 = 3298 = 
Cl * 35 13 35 5 - 9896 = 

Tin Chloride 

Sn 
Cl 



45 26 per cent - 117 4 = 384 
54 74 35 5 = * 542 



Ratios 

I 

3 



4 04 



The formula of the gold chloride is AuCls, and of the tin chloride, 
SnCU 

Magnesium carbonate on analysis may yield: C= 14.26, Mg= 28 37; 
Fe=.34, 0=5703, or, if recorded m the form of oxides: 002=52.24, 
MgO=47 25, FeO= 43 From either of these results the formula is 
easily obtained by the method described. 



C=i4 2611 97=1 188=1 009, 

Mg= 28 37- 23.94= i 186=1.000, 

Fe~ .34-5588= .006= .006, 

0=57.03-15 96=3 573=3-i2, 



or, 

MgCOs, if we neglect the small 
quantity of iron present 



10 GENERAL CHEMICAL MINERALOGY 

From the second set of figures we have* 

0)2=5224-4389=1 19 = 1, ] or > 

MgO=47 25 3990=1 184=1, r MgO C02, which is the same as 
FeO= 437184= 006, J MgCOs, written in a different way 

All formulas are derived by methods like these, but in many cases 
the processes are made more difficult by the impossibility of deciding 
positively whether those substances that are present in small quantities 
are present as impurities or whether they exist as essential parts of 
the compound 

Formulas of Substances Containing Two or More Metallic 
Elements or Acid Groups. In the illustration given above the com- 
pounds consist of but one kind of metallic element combined with one 
kind of acid Often in the case of minerals there are present two or 
more metallic elements, and less commonly several acid groups. When 
two metals are present in definite atomic proportions the formula is 
written in the usual manner, as CaMg(COs)2 for the mineral dolomite, 
in which calcium and magnesium are present in the ratio of one atom 
of each to two parts of the acid group COa. Very often, and perhaps in 
the majority of cases, when two or more metallic elements are present 
in different specimens of a mineral they are not found always in the 
same proportion the mineral may consist of isomorphic mixtures 
of several substances For instance, many calcium-magnesium car- 
bonates are known in which the ratio of calcium to magnesium present 
is not as i atom to i atom, but in which this ratio is as 2 atoms 
to i atom, 3 atoms to 2 atoms, or a ratio which would have to be 
represented by irrational figures like 2 7236 atoms to i 5973 atoms 
Each one of these compounds properly requires a separate formula, 
as aCaCOa+MgCOs, 3CaC0 3 +2MgCO 3 , etc , but practically the entire 
series of compounds is represented by a single symbol, thus (Ca Mg) COs, 
indicating that in the series we have to do with mixtures of carbonates 
of calcium and magnesium, or with complex molecules containing in 
different instances different proportions of the two carbonates. For 
greater defimteness the symbol of the characteristic element of the 
substance which is in largest quantity in the compound is usually written 
first, as (Ca Mg)COs, when calcium carbonate is m excess, or 
(Mg Ca)COs when pnagnesmm carbonate predominates If still greater 
defimteness is desired small figures are placed below the symbols of the 
elements concerned, as (Ca2 Mgi)COs or (Ca 3 Mg2)C03, to indicate 
the respective proportions present. (Ca2 Mgi)COs signifies that the 



COMPOSITION AND CLASSIFICATION 11 

mineral thus represented contains calcium and magnesium in the 
ratio of 2 atoms of the former to i of the latter 

Compounds Containing Water. Often salts that separate from 
aqueous solutions combine with certain definite proportions of water 
Sometimes this water combines with the anhydrous portion of the com- 
pound to form a double salt, as MgSO4+ 7 H 2 0, or MgS0 4 7H 2 
At other times a portion of the water, in the form of the group (OH), 
called the hydroxyl group, occupies the pl ace usua lly occupied by 
a metallic element, and, occasionally, that usually occupied b> an 
acid group, or by oxygen, as in Mg(OH)2 

Water of Crystallization. Double salts composed of an anhydrous 
portion combined with water are usually well crystallized Although 
the water appears in many cases to be but loosely combined with the 
remainder of the compound it is an essential part of its crystal particle, 
for by the loss of even a portion of it the crystal system of the compound 
is often changed Water in this form is known as water of crystalliza- 
tion, and the compounds are designated hydrates 

The magnesium sulphate MgSO* 7 H aO forms orthorhombic crystals 
By evaporation of a hot solution of this substance the sulphate 
MgSO4 6H20 separates as monochmc crystals. 

Gypsum is CaSOi 2H 2 O Its crystallization is monoclinic When 
heated to 200 it passes into the anhydrous orthorhombic mineral 
anhydrite, CaS04 

Water of crystallization may frequently be driven from the com- 
pound in which it exists by continued heating at a comparatively low 
temperature. It is usually given off gradually an increase in the tem- 
perature causing an increase in the quantity of water released until 
finally the last trace disappears In many instances such a very high 
temperature is required to drive off the last traces of the water that it 
would appear that some of it is held m combination in a different 
manner from that in which the remainder is held Indeed, it is not at 
all certain that double salts containing water of crystallization are 
different in any essential respect from ordinary atomic molecules in 
which hydrogen and oxygen are present in atomic form. 

Combined Water. Water of crystallization is thought of as 
existing in the compound as water because of the ease with which it 
can be driven off Compounds in which the hydroxyl group is present 
yield water only upon being heated to comparatively high temperatures 
In them the elements of water are present, but not united as water. 
When freed from their combinations with the other constituents of the 
compound by heat they unite to form water Because its elements 



12 GENERAL CHEMICAL MINERALOGY 

are thought of as closely combined with the other elements in the 
molecule, this kind of water is often distinguished from water of crystal- 
lization by the term combined water. 

Bructte (Mg(OH) 2 ) and malachite (Cu2(OH) 2 C0 3 ) are minerals 
containing the elements of water When heated they yield water 
according to the reactions Mg(OH) 2 = MgO+H 2 O and Cu 2 (OH) 2 COs 
= CuO+CuC0 3 +H 2 0. 

Combined water is not only more difficult to separate from its com- 
bination than is water of crystallization, but when the combination 
is broken the chemical character of the original substance is radically 
changed, as may be seen from the reactions above indicated. More- 
over, combined water is given off suddenly, at a certain minimum 
temperature, and not gradually as in the case of water of crystal- 
lization. 

Blowpipe Analysis. Although blowpipe analysis serves merely to 
identify the chemical components of minerals, it is a most important 
aid to mineralogists in their practical work 

Nearly all minerals may be recognized with a close degree of accu- 
racy by their morphological and physical properties To distinguish 
between several minerals that are nearly alike in these characteristics, 
however, the determination of composition is often important In" 
cases of this kind a single test made with the blowpipe will frequently 
give the desired information as to the nature of some one or more of 
the chemical elements present, and thus in a few moments the mmeial 
may be identified beyond mistake 

The apparatus necessary to perform blowpipe analysis is very 
simple and the number of pieces few These, together with all the 
reagents in sufficient quantity to determine the composition of hundreds 
of minerals, may be packed into a box no larger than a common lunch 
box (See pp 467-470) 

For more refined work than the mere testing of minerals a larger 
collection of both apparatus and reagents is necessary, but it no case 
is the quantity of material consumed in blowpipe analysis as great as 
when wet methods of analysis are used 

Principles Underlying Blowpipe Analysis. The principal phe- 
nomena that are the basis of blowpipe work are the simple ones known 
in chemistry as volatilization, reduction, oxidation, and solution 

For volatilization experiments charcoal sticks and glass tubes are 
used A blowpipe serves to direct a hot blast upon the assay. The 
volatilized products collect on the cool parts of the charcoal which 
they coat with a characteristic color, or upon the cooler portions of 



COMPOSITION AND CLASSIFICATION 13 

tlie glass tubes The sublimates that collect in the tubes may be tested 
with reagents or examined under the microscope 

Some volatile substances impart a distinct and characteristic color 
to an otherwise colorless flame These may be tested in the direct flame 
of the blowpipe 

Oxidation and reduction experiments are usually performed either 
on charcoal or in glass tubes Oxidations are effected in open tubes 
and reductions in those closed at one end The products of the oxida- 
tion or of the reduction are studied and from their characteristics the 
nature of the original substance is inferred 

The solution of bodies to be tested is often made in the usual man- 
ner, i.e , by treatmg them with liquid reagents, but more frequently 
it is accomplished by fusion of a small quantity of the body with borax 
(Na 2 B 4 07 ioH 2 0) or microcosmic salt ((NH4)NaHPO4 4H 2 Q). The 
molten reagent dissolves a portion of the substance to be tested and in 
many cases forms with it a colored mass From the color of the mass 
the nature of the coloring matter may be learned. 

Although the underlying principles of blowpipe analysis are simple 
the reactions that take place between the reagents and the assay are 
often very complex. 

More explicit details of the operations of qualitative blowpipe 
analysis are given in Part III 

Microchemical Analysis. The processes of microchemical analysis 
are limited in their application to the detection of a single element or, 
at most, of a very few elements in small quantities of minerals. They 
are employed mainly in deciding upon the composition of a substance 
whose nature is suspected 

The principle at the basis of all microchemical methods is the manu- 
facture of crystallized precipitates by treatment of the mineral under 
investigation with some reagent, and the identification of these pre- 
cipitates through their optical and morphological properties. 

In practice, a small particle of the mineral the nature of which it 
is desired to know is placed on a small glass plate, which may be covered 
with a thin film of Canada balsam to prevent corrosion, and is 
moistened with a drop or two of some reagent that will decompose 
it The solution thus formed is slowly evaporated by exposure to the 
air The plate is then placed beneath the objective of a microscope 
and the crystals formed during the evaporation are investigated Or, 
after a solution of the assay is obtained there is added a small quantity 
of some reagent and the resulting precipitate is studied under the 
microscope. By their shapes and optical properties the nature of the 



14 GENERAL CHEMICAL MINERALOGY 




FIG i Sodium Fluosilicate Crystals Magnified 72 diam (After Rosenbusch ) 




FIG 2 Potassium Fluosihcate Crystals Magnified 140 diam, (After Rosenbusch ) 



COMPOSITION AND CLASSIFICATION 15 

crystals produced is determined, and in this way the nature of the con- 
stituents they have obtained from the mineral particles is discovered 

A large number of reagents ha\ e been used m microchemical tests 
each of which is best suited to some particular condition The most 
generally useful one is hydrofluosihcic acid (H 2 SiF b ). If small frag- 
ments of albite and of orthoclase are placed on separate glass slips, such 
as are used for mounting microscopic objects, and each is treated with 
a drop of this reagent and then allowed to remain in contact with the 
air lor a few minutes until the solutions begin to evaporate, those 
portions of the solutions remaining will be discovered to be filled with 
little crystals The crystals in the solution surrounding the albite are 
hexagonal m habit (Fig i), while those in the solution surrounding 
the orthoclase are cubes, octahedrons or combinations of forms belonging 
to the isometric system (Fig 2). The former are crystals of sodium 
fluosihcate and the latter crystals of the corresponding potassium salt 
The albite, consequently, is a sodium compound and the orthoclase a 
compound of potassium In similar manner, by means of this or of 
other reagents the constituents of many minerals may be easily detected 
The method, however, is made use of only in special cases, when for 
some reason or other analytical methods are not applicable 

Synthesis. Synthesis is the opposite of analysis. By the analytical 
processes compounds are torn apart, or broken down, whereas by syn- 
thetical operations they are put together or built up Synthetic methods 
are employed principally in the study of the constitution of minerals 
and of their mode of formation, and in the investigation of the condi- 
tions that determine the different crystal habits of the same mineral 
The products of synthetic reactions are often spoken of as artificial 
minerals because made through man's agency In many instances 
these artificial minerals are identical in every sense with natural minerals 
Consequently, they may often serve as material for study, when the 
quantity of the natural mineral obtainable is too small for the purpose 

Classification of Minerals. Classification is the grouping of 
objects or phenomena in such a manner as will bring together those 
that a're related or that are similar in many respects and will separate 
those that are different 

Since minerals are chemical compounds whose properties depend upon 
their compositions, then* most logical classification must be based upon 
chemical relationships. But their morphological and physical properties 
are their most noticeable features, and hence these should also be taken 
into account in any classification that may be adopted. Probably 
the most satisfactory method of classifying minerals is to group them, 



16 GENERAL CHEMICAL MINERALOGY 

first, in accordance with their chemical relationships and, second, m 
accordance \\ith their morphological and physical properties 

The first division is into the great chemical groups, as, for instance, 
the elements, the chlorides, the sulphides, etc The second division 
is the separation of these great groups into smaller ones comprising 
minerals possessing the same general morphological features These 
smaller groups may contain only a single mineral or they may contain 
a large number of closely allied ones If the basis of the subgroupmg 
is manner of crystallization, it follows that the members of subgroups 
containing more than one member are usually isomorphous compounds 
Thus the subdivisions of the great chemical groups are single minerals 
and small or large isomorphous groups of minerals, arranged in the 
order in which their metallic elements are usually discussed in treatises 
on chemistry For example, the great group of carbonates embraces 
all minerals that are salts of carbonic acid (EfeCO'j) This great group 
is divided into smaller groups along chemical lines, as for instance, the 
normal carbonates, the hydrous carbonates, the basic carbonates, etc 
These smaller groups are finally divided into subgroups according to 
their morphological properties the normal salts, for example, being 
divided into the two isomorphous groups known as the calcite and the 
aragonite groups, and a third group comprising but a single mineral 

In certain specific cases some other classification than the one 
outlined above may be desirable For instance, in books written for 
mining students it is often found that a classification based upon the 
nature of the metallic constituent is of more interest than the more 
strictly scientific one outlined above, because such a classification 
emphasizes those components of the minerals with which the mining 
student is most concerned In books written for the student of rocks, 
on the other hand, the most important determinative features of minerals 
are their morphological characters, hence m these the classification 
may be based primarily on manner of crystallization 

In the present volume the classification first outlined is used, but 
because such a small proportion of the known minerals are discussed 
the beauties of the classification are not as apparent as they would be 
were ail described 



CHAPTER II 
THE FORMATION OF MINERALS AXD THEIR ALTERATIONS 

The Origin of Minerals. Minerals, like other terrestrial chemical 
compounds, are the result of reactions between chemical substances 
existing upon the earth When they are the direct result of the action 
of elements or compounds not already existing as minerals they are said 
to be primary products, when formed by the action of chemical agents 
upon minerals already existing they are often spoken of as secondary, 
though this distinction of terms is not always applied 

Quartz (SiCb), formed by the cooling of a molten magma, is pnmar> , 
when formed by the action of water upon the siliceous constituents of 
rocks it is secondary 

The Formation of Primary Minerals Minerals are produced in a 
great variety of ways under a great variety of conditions Even the 
same mineral may be produced by many different methods The more 
common methods by which primary minerals are formed are precipita- 
tion from a gas or a mixture of gases, precipitation from solution, the 
cooling of a molten magma, and abstraction from water or air by plants 
and animals 

Deposits from Gases. Emanations of gases are common in vol- 
canic districts The gases escaping from volcanic vents are mainly 
water vapor, hydrochloric acid, sulphur dioxide, sulphuretted hydro- 
gen, ammonia salts and carbon dioxide, besides small quantities of other 
gases and the vapors of various metallic compounds By the reactions 
of these with one another or with the oxygen of the air, sulphur, salam- 
momac (NHiCl) and other substances may be formed, and by their 
reaction upon the rocks in the neighborhood halite (NaCl), ferric chlo- 
ride (FeCls), hematite (Fe20s) and many other compounds may be 
produced 

The production of minerals through the reactions set up between 
various gases and vapors is known as pneumatolysis Their separation 
from the gaseous condition is known as sublimation Minerals formed 
by sublimation are usually deposited as small, brilliant crystals on the 
surfaces of rocks or upon the walls of cavities and crevices in them. 

17 



18 GENERAL CHEMICAL MINERALOGY 

The reactions by %\hich they are produced are often quite simple. Thus 
the reaction between sulphuretted hydrogen and sulphur dioxide yields 
sulphur (2H2S+S02 = 3S+2H20), as does also the reaction between the 
first named gas and the oxygen of the atmosphere (HjS+O = H2O+S) 
Ferric chloride may be produced by the action of hot hydrochloric 
acid upon some iron-bearing material deep within the earth's in- 
terior This being volatile at high temperatures escapes to the air 
as a gas Here it may react with water vapor, with the resulting for- 
mation of hematite (2FeCl3+3H 2 0=Fe203+6HCl) By the action 
of carbonic acid gas upon volatile oxides, carbonates are formed, 
(Fe203+2C02=2FeCOa+0) In other cases, however, the reactions 
are very complicated 

Precipitation from Solution. Nearly all substances are soluble 
to an appreciable degree in pure water An increase in temperature 
usually increases the quantity of the substance that can be dissolved, 
as does also an increase of pressure Moreover, the solubility of a 
salt is increased on the addition of another salt containing no common 
ion, and, conversely, is diminished in the presence of another having a 
common ion Thus, gypsum (CaS04 2H20) is sparingly soluble in 
water, but it becomes much more soluble upon the addition of salt 
(NaCl) On the other hand, salt (NaCl) is much less soluble in water 
containing a little magnesium chloride (MgClo) than it is in pure water. 

When a solvent contains a maximum amount of any substance that 
it may hold under a given set of conditions the solution is said to be 
saturated From a saturated solution under ordinary conditions 
precipitation results Upon the evaporation of the solvent, the lowering 
of its temperature or of the pressure under which it exists, or the addi- 
tion to the solution of a substance containing an ion already in the 
solution. Of course, the addition of a substance which will react with 
the solution and produce a compound insoluble m it will also cause 
precipitation 

The following table contains the results of various experiments on 
the solubility of some common minerals 

SOLUBILITY OF VARIOUS COMPOUNDS IN 100 PARTS PURK WATFR 
(The results are given in parts by weight) 

Halite (NaCl), at 7 35 68 Calcitc (CaCO,), in the 
Fluonte (CaF 2 ), at 15^ 0037 cold 002 

Gypsum (CaS0 4 2H 2 0),ati5 250 Strontiamte (SrCO,) in 
Anhydrite (CaS0 4 ), in the cold 00025 the cold 00555 

Celestite (SrS0 4 ), at 14 015 Magnetite (F t e() 4 ) 00035 



FORMATION OF MINERALS 19 

PERCENTAGES OF VARIOUS MINERALS SOLUBLE IN WATER \T 80 

(When treated 30 to 32 da\s) 

Galena (PbS) 179 Chalcop>nte CCuFeS 2 ) 1669 

Stibmte (Sb 2 S 3 ) 5 01 Bouraomte f(Pb Cu)SbS 3 ) 2 075 

Pynte (FeS 2 ) 2 99 Arsenopynte (FeAsSj i 5 

Sphalerite (ZnS) 025 

So many substances that are usually regarded as insoluble are known 
to be dissoh ed under conditions of high temperature and pressure that 
no substance is behe\ ed to be entirely insoluble 

Po\\dered apophylhte ((HK) 2 Ca(Si0 3 )2 H 2 0), which is a silicate 
that is generally regarded as insoluble in water, is dissoh ed sufficiently 
in this sohent at a temperature of i8o-iQO and under a pressure of 
10-12 atmospheres to }ield crystals of the same substance upon cooling 

Water containing gases or traces of salts is usually a more efficient 
dissolving agent than pure water When the gases are lost, or the 
salts are decomposed by reactions with other compounds, precipitation 
may ensue 

PARTS OF VARIOUS MINERALS DISSOLVED ix 10,000 PARTS OF VARIOUS 

SOLUTIONS 

Gold loses i 23 per cent of its \\eight when treated with 10 per cent soda 
solution at 200 

One part gypsum (CaSO 4 2H 2 0) dissolves in 199 parts of saturated NaCl 
solution Only 4 part dissolves in 200 parts pure \\ater 

Pyt lie (FeSo) loses 10 6 per cent of its mass upon boiling for a long time 
with a solution of Na 2 S Under the same circumstances galena loses 2 3 
per cent 

One of the commonest of the gases found in water on the earth's 
surface is carbon dioxide This is an active agent in decomposing sili- 
cates and in dissolving carbonates, so that water m which it is dissolved 
is usually a more powerful solvent than pure water Its dissolving 
power increases with the pressure, as in the case of pure water, but 
diminishes with increasing temperature The action of carbonated 
water on silicates is due to the replacement of the silicic acid by carbonic 
acid and the production of bicarbonates, which are usually more soluble 
than the corresponding carbonates The greater solubility of carbon- 
ates, like calcite, in carbonated water is also due to the formation of 
bicarbonates For example, the action of carbonated water upon cal- 
cite (CaCOs) is as follows 

CaC03+H 2 0+C0 2 =CaIfc(C03)2. 



20 GENERAL CHEMICAL MINERALOGY 

Carbonated water is more effective as a solvent under pressure 
because of the inability of the CCb to escape under this condition When 
pressure is removed the CCb escapes, or evaporation takes place, and the 
reverse reaction occurs, as 

CaH 2 (C0 3 )2= CaC0 3 +H 2 0+CO 2 

The dissolving effect of carbonated water upon various carbonates 
and other minerals and the influence of pressure and temperature upon 
the solution of a carbonate are indicated in the three tables following 

SOLUBILITY OP CERTAIN CARBONATES IN 10,000 PARTS OF CARBONATED 

WATER 

(The results are given in parts by weight) 

Calcite (CaC0 3 ), at 10 10 o Sidente (FcCO,) at 18 7 2 

Dolomite (CaMg(CO s ) 2 ) at 18 3 i Witherite (BaCOj) at 10 170 

Magnesite (MgCOs), at 5 13 i Strontiamte (SrCOi), at 10 12 o 

PERCENTAGES OF \ARIOUS MINERALS SOLUBLE IN CARBONATFD WATLR 

(When treated 7 weeks) 

Adulana (KAlSiaOs) 328 Apatite (Ca(F CIXPCX).) i 821 

Ohgoclase Apatite (Ca fi (F Cl)(POi)0 2 018 

(NaAlSi 3 8 + CaAl(SiO) 4 ) 533 Olivme ((Mg Fe) 2 Si0 4 ) 2111 

Hornblende (complex silicate) i 536 Magnetite (Fe 3 4 ) 307 to i 821 
Serpent] ne (KUMgsSi'Oo) i 211 

INFLUENCE OF TEMPERATURE AND PRESSURE UPON THE SOLUTION OF 
MAGNESIUM CARBONATE (MgC0 3 ) IN CARBONATED WATER 

(The results are given m parts per 10,000 by weight) 

i atmos at 19 2 579 parts Temp 13 4 under i atmos 2 845 parts 
32 3 730 29 3 2 105 

56 4 620 62 o i 035 

75 5 120 82 o 400 

90 5 659 100 o ooo 

Precipitation from Atmospheric Water Rain is an active agent 
in dissolving mineral matter Since it absorbs small quantities of carbon 
dioxide, sulphur gases and other substances as it passes through the 
atmosphere it may act upon many compounds, dissolving some, decom- 
posing others and forming soluble compounds from those that would 
otherwise be practically insoluble Moreover, it transports the dissolved 
materials from one portion of the crust to some other portion, where, 
under favorable conditions, they may be precipitated The rain water 
that penetrates the earth's crust, dissolving and precipitating in its 



FORMATION OF MINERALS 



21 



course through the crust, is known as vadose water It is an important 
agent in ore-formation, since it may collect mineral matter from a great 
mass of rocks and precipitate it in some favorable place, thus making 
ore bodies 

Deposits of Springs. Springs are the openings at which under- 
ground \\ater escapes to the earth's surface Much of the water flowing 
from springs is the meteoric water which has circulated through the 
crust and is again seeking the surface In its course through the crust it 
dissolves certain materials Where it reaches the surface some of this 
material may be dropped in consequence of (i) evaporation of the \\ater, 
or (2) the escape of carbon dioxide, or (3) the oxidation of some of its 
constituents through the action of the air, or (4) the cooling of the water 
in the case of warm or hot springs 

The deposits thus formed may occur as thin coatings on the rocks 
over which the spring water passes, or as layers in the bottom of the 
spring and the stream issuing from it Among the commonest minerals 
thus deposited are calcite (CaCOs), aragomte (CaCOs), siderite (FeCOs) 
and other carbonates, gypsum (CaSO-i 2H20), pynte (FeS2), sulphur 
(S), and limonite (Fe4O3(OH) 6 ) The carbonates are deposited largely 
in consequence of the escape of C02 from the water, gypsum in conse- 
quence of cooling, and limonite and sulphur through oxidation. If the 
water contains EkS, this reacts 
with the oxygen and a deposit _ 4 j, 
of sulphur ensues (compare 
P 18) 

When the precipitation oc- 
curs m cracks or fissures in the 
rocks the precipitated matter 
may partially or completely fill 
the fissure, producing a vein, or, 
the precipitated matter may fill 
an irregular cavern forming a 
bonanza It sometimes covers 
the walls of cavities or the sur- 
faces of minerals already exist- 
ing, giving rise to a druse In 
other cases precipitation may 
occur while the solution is dripping from an overhanging surface, 
making a stalactite, or the precipitate may fill the tiny crevices between 
grains of sand cementing the loose mass into a compact rock 

Mmerals produced by precipitation are often beautifully crystallized. 




FIG 3 Cross-section of Symmetrical Vein 
(Aflts Le Neue Foster ) 

(a) Decomposed rock ($) Galena 

(6) Quartz crystals (d) Sidente 



22 GENERAL CHEMICAL MINERALOGY 

At other times they form groups of needles yielding globular and other 
imitative shapes, while in still other instances they occur as pulverulent 
or amorphous masses The fillings of veins are often arranged sym- 
metrically, similar materials occurring on opposite sides of their central 
planes in bands, as shown in the figure (Fig 3) Some important ores 
have been concentrated and deposited in this way 

Deposits from Hot Springs.- The water of hot springs deposits a 
greater variety of minerals than that of cold springs Practically all 
minerals that are soluble in hot water or in hot solutions of salts are 
among them Among those of economic value may be mentioned 
cinnabar (HgS) and stibnite (Sb2Ss) 

Deposits from the Ocean and Lakes. The water of the ocean and 
of many lakes is rich in dissolved salts. That of lakes, however, is often 
saturated or nearly so, while that of the ocean is not near the saturation 
point. Consequently, while many lakes may deposit mineral sub- 
stances, the ocean does not do so except under peculiar conditions When 
a portion of the ocean is separated from the mam body of water, it may 
evaporate and leave all of its mineral matter behind Lakes may also 
completely evaporate with a similar result In each case the deposits 
form layers or beds at the bottom of the basin in which the water was 
collected. 

In other instances the water brought to the ocean or a lake may 
contain substances which will react with some of the materials already 
present and produce an insoluble compound which will be precipi- 
tated 

Of course, the nature of the beds thus formed will depend upon the 
character and proportions of the substances that were in the water 
The ocean will yield practically the same kinds of compounds all over 
the world and the beds deposited by the evaporation of ocean water 
will be formed in nearly the same succession everywhere In the case 
of enclosed bodies of water like lakes or seas in which the composi- 
tion of the water may differ, the deposits formed may also differ 

Many of the deposits formed in bodies of water are of great eco- 
nomic importance and, consequently, are extensively worked Prob- 
ably the most important are the beds of salt (NaCl) and of gypsum 
(CaSO 4 2H 2 0), although borax (Na 2 B 4 7 ioH 2 0) was foimerly 
obtained in large quantity from the deposits of some of the lakes in 
the desert portions of the United States 

In the following table are given the results of analyses of water of 
the ocean and of Great Salt Lake, in Utah, calculated on the assump- 
tion that the elements are combined in the manner indicated m the 



FORMATION OF MINERALS 



23 



column on the left The results of the analyses of the waters of a few 
noted lakes are given in the succeeding table 

COMPOSITION OF SAXTS CONTAINED IN WATER OF THE OCEA.N AND GRE\T 



NaCl 

KCI 

MgCL 

CaS0 4 

MgS0 4 

Na 2 S0 4 



LAKE 
(Parts in 1000 of Water) 

I II 

27 3726 8 1163 

5921 1339 

3 3625 6115 

1 3229 9004 

2 2437 3 0855 



RbCl 2 

MgBr 2 

Ca 3 (P0 4 ) 2 

CaC0 3 

FeC0 3 

Si0 2 



0190 

0547 
0156 

0434 
0019 
0149 



0034 
0081 

0021 
0780 
OOII 

0024 



in 

118 628 

14 908 
858 

9 321 
5 363 

tr 



35 0433 



12 9427 



149 078 



I Water of N Atlantic off Norwegian Coast Anal>st, C Schmidt 
II Average of Five Analyses, Caspian Sea at depths of from i m to 640 m 

Analyst, C Schmidt 
III Great Salt Lake, Utah Analyst, O D Alien 

PERCENTAGE COMPOSITION or THE RESIDUES OF A FE\\ LAKE WATERS 





Cl 


Br 


S0 4 


C0 3 


Na 


K 


Ca 


Mg 


Si0 2 

etc 


Total Solids 
(per 1000 
of Water) 


Dead Sea 
Lake Beisk, Siberia 
Qoodenough Lake, B C 
Borax Lake, Cal 


64 49 
22 79 
7 64 
32 27 


1 45 

tr 

04 


45 
42 32 

7 OS 
13 


61 
41 41 
22 47 


15 75 
31 32 
36 17 
38 10 


3 24 
1 01 
6 65 
1 52 


4 09 
07 
02 
03 


10 53 
1 86 
04 
35 


tr 
02 
99 
02 


220 3 
104 7 
103 47 
76 56 



Deposits from Magmatic Water. Equally important in depositing 
mineral matter is the water that escapes from cooling lavas and other 
molten magmas designated as juvenile water All molten magmas 
existing under pressure, i e , at some distance beneath the crust, contain 
the components of water, which escape as the magma cools or when the 
pressure diminishes, whether the diminution of the pressure is due to 



24 GENERAL CHEMICAL MINERALOGY 

the escape of the lava to the surface or to the cracking of the crust 
In its passage to the surface the hot water carrying dissolved salts pene- 
trates all the cracks and cavities in the rocks through which it passes 
in its ascent and deposits its burden of material, forming veins and other 
types of deposits Or, its components may decompose the materials 
with which it comes in contact, replacing them wholly or in part by the 
substances which it is carrying or by the products of decomposition 




FIG. 4 Cross-section of Vein in Green Porphyry The vein filling is chalcedonj 
The white splotches are feldspar crystals The fairly uniform character of the 
rock where not affected by the vein is seen on the right side of the picture The 
rude banding parallel to the vein is due to changes that have proceeded out- 
ward from the vein-mass into the rock 

Since in many cases magmatic water contains corrosive gases, such as 
fluorine, its action on the rocks which it traverses is profound A tiny 
crack in the rocks may be gradually widened and the material on both 
sides of it be replaced by new material, thus producing a vein which 
is sometimes difficult to distinguish from a vein made in other ways 
(Fig 4) This process is known as metasomatism, which is one kind of 
metamorphism It is an important means of producing pseudomorphs 
and bodies of mineral matter sufficiently rich in metallic contents to 
constitute ore-bodies 



FORMATION OF MINERALS 25 

Solidification from Molten Magmas. A molten magma, such as a 
liquid lava, is probably a solution of various substances mainly sili- 
cates in one another, or in a hot solvent Upon cooling or upon change 
of conditions, such as may arise from loss of gas or water or from reduc- 
tion of pressure, this hot solution graduall} deposits some of its con- 
stituents as definite chemical compounds Upon further cooling other 
compounds solidify and so on, until finally, if the rate of cooling has been 
slo\\, the entire mass may separate as an aggregate of minerals such 
as constitute many of the rocks, as granite for instance, and main of the 
lavas If the cooling has been rapid, some of the material ma\ separate 
as definite minerals \\hile the remainder solidifies as a homogeneous 
glass, as in the case of most lavas Sometimes the minerals thus formed 
are bounded by crystal planes, but usually their growth has been so 
interfered with that it is only by their optical properties that they can 
be recognized as crystalline substances The nature of the minerals 
that separate depends upon a great variety of conditions, the most 
important of which is the chemical composition of the magma 

In some cases the minerals separating from a magma tend to segre- 
gate m some limited portion of its mass and thus produce an accumula- 
tion that may be of economic value, le, the magma dijf a entities 
Magnetite (FesGO, ilmenite ((Fe Ti) 2 3 ), pynte (FeS 2 ) and a few other 
minerals are sometimes segregated in this way in very large masses 

Metamorphic Minerals Many minerals are characteristic of rocks 
that are in contact with others that were once molten They were 
formed by the gases and hot waters given off from the magmas before they 
cooled The hot solutions with their charges of gas and salts penetrated 
the pores of the surrounding rock and deposited in them some of their 
material They reacted with some of the rock's components, producing 
new compounds, and extracted others, leaving pores into which new 
supplies of gas and water might enter In some cases the entire body 
of the surrounding rock has been replaced by new material for some 
distance from the contact Beyond this belt of most profound meta- 
morphism are other belts in which the rock is less altered, until finally in 
the outer belt is the unchanged original rock Into the outer contact 
belt perhaps only gas penetrated and the changes here may be entirely 
pneumatolytic Near the contact the changes may be metasomatic 
Minerals formed by these processes near the contact of igneous masses 
are frequently referred to collectively as contact minerals. 

In other cases new minerals may be produced in rocks in consequence 
of crushing attended by heat Hot water under high pressure 
greatly facilitates chemical changes A part of the materials of the 



26 GENERAL CHEMICAL MINERALOGY 

crushed rock dissolves, reactions are set up and new compounds may 
be formed The new minerals produced are more stable than the 
original ones and have in general a greater density and consequently 
a smaller volume The type of metamorphism that produces these 
effects is kno\\n as dynamic metamot phtsm 

Organic Secretions. The transfer of mineral substances from a 
state of solution to the solid condition is often produced through the aid 
of organisms Mollusca, like the oyster, clam, etc , crustaceans, like 
the lobster or crab, the microscopic animals and plants known as pro- 




FIG 5 Diorite Dike Cutting Granite Gneiss Pelican Tunnel, Georgetown, Colo. 
(After Sptirr and Garry ) 

tozoans and algae and many other animals and vegetables abstract 
mineral matter from the water in which they live and build up for them- 
selves hard parts These hard parts, usually in the form of external 
shells, are composed of calcium carbonate (CaCOs), either as calcite or 
aragomte, of silica (8102) or of calcium phosphate Cas(P04)2. Although 
not commonly regarded as minerals these substances are identical 
with corresponding substances produced by inorganic agencies l 

Paragenesis. It is evident that minerals produced in the same 

1 Plants and animals upon decaying yield organic acids which may attack minerals 
already existing and thus give nse to solutions which may deposit pynte (FeSa), 
hmomte (a hydrated iron oxide) or some other metallic compound This process, 
however, is properly simply a phase of deposition from solutions 



FORMATION OF MINERALS 27 

\\ay \\ ill generally be found together. A certain association of minerals 
will thus characterize deposits from magmas, another association 




FIG 6 Vein in Griffith Mine, Georgetown Colo , Showing Two Periods of Vein 
Deposition (After Spwr and Garry ) 

gn = wall rock 6 = sphalerite c chalcopynte 

ff = comb quartz p = pynte g = galena 

Balance^of vein-filling is a mixture of manganese-iron carbonates 



15 




10 



It \Z 



13 SH- 



FIG 7 Vein Forming Original Ore-Body, Butte, Mont (After W.H Weed) 

(i) Fault breccia, (2) ore, (3) altered granite, (4) first-class ore, (5) crushed quartz and 

bormte, (6) fault clay, (7) solid pyrite and bormte, (8) crushed quartz and pynte, (9) solid 

enargite ore with bormte, (10) banded white quartz and bormte, (n) white quartz, 6 inches, 

(12) solid bormte, (13) solid pynte with bormte and quartz blotches, (14) bormte, (15) granite. 

those precipitated from water, another those produced by contact 
action, etc This association of minerals of a similar origin is known 



28 



GENERAL CHEMICAL MINERALOGY 



as their paragenesis From a study of their relations to one another the 
order of their deposition may usually be determined 

Occurrence. The manner of occurrence of mineral substance is 
extremely varied, as may be judged from the consideration of the vari- 
ous ways in which they are formed Deposits laid down in water occur 
in beds or in the cement uniting grains of sand, etc , such as the beds 
of salt (NaCl) or gypsum (CaSO* 2H 2 0) found in many regions Those 
produced by the cooling of magmas may form great masses of rock 
such as granite, \vhich when it occurs as the filling of cracks in other 
rocks is said to have the form of a dike (Fig 5) Deposits made by 

water, whether meteoric or mag- 
matic may give rise to veins, which 
may be straight-walled or branch- 
ing, like the veins of quartz (Si02) 
that are so frequently seen cutting 
various siliceous rocks When the 
veins aie filled by meteoric water 
they often have a comb-structure 
the filling consisting of several sub 
stances arranged in definite layers 
following the vein walls (see p 21) 
If the composition of the depositing 
solution, whether meteoric or mag- 
matic, has remained constant for a 
long time the vein may be filled 
with a single substance It its com- 
position changed during the time 
the filling was in progress the layers 
are of different kinds Further, it 
deposition continued uninterruptedly 
the layers may match on opposite 
sides of the vein and the succession 
may be the same from walls to center If, however, after the partial 
or complete filling of the crack it was reopened and the new crack was 
filled, the new vein when filled would be unsymmetncal if the new crack 
occurred to one side of the center of the original vein (Fig 6) Repeated 
reopening may give rise to a vein that is so lacking in symmetry that 
it is difficult to trace the succession of events by which it was produced 
(Fig 7) Veins filled by magmatic water are frequently more homo- 
geneous. 

Druses (Fig 8) arise when deposits simply coat the walls of fissures. 




FIG 8 Druse of Smithsomte (ZnCO 3 ) 
on Massive Smithsomte 



FORMATION OF MINERALS 



29 



In many cases they may be regarded as veins, the development of which 
has been arrested and never completed When the deposits coat the 
walls of hollows within rocks they are known as geodes (Fig 9) Geodes 
are common in limestones and other easily soluble rocks in \*hich 
cavities may be dissolved 

Gases and water under great pressure may penetrate the micro- 
scopic pores existing in all rocks and there deposit material which may 
fill the pores and cement the rocks If the deposited material is metallic 
the rocks may be transformed into masses sufficiently rich in metallic 
matter to become ore-bodies A body of this kind is known as an 
impregnation It is well represented by some of the low grade gold 
ores, such as those in the Black Hills 

When rocks are decomposed bv the weather they are broken up 




FIG 9 Geodes Containing Calcite (CaCOs) Crystals 

The rains wash the disintegrated substance into streams In its course 
downward to lakes or the ocean, the heavier fragments, such as metallic 
particles, may settle while the lighter portions are carried along 
Thus the heavy parts may accumulate in the stream bottoms These 
materials, consisting of gold, magnetite, garnet, pyrite and other min- 
erals of high specific gravity, form a loose deposit m the stream bed 
which is known as a placer. Gold is often found in placer deposits 
The lighter portions may be carried to the lake or sea into which the 
streams enter and may accumulate as sand on beaches and on the 
bottom near the shores as gravel, sand, silt, etc Most sand consists 
principally of quartz, but many sands contain also grains of feldspar 
and other silicates, and sometimes other compounds 



30 GENERAL CHEMICAL MINERALOGY 

Alteration of Minerals. Minerals, like living things, are constantly 
subject to change Circulating waters may dissolve them in part, 
or completely, and transport their material to a distant place, there 
depositing it either in the form it originally possessed or in some new 
form On the other hand, the mineral substance may be decomposed 
into several compounds some of which may be carried off, while others 
are left behind Again, the material remaining behind may com- 
bine with other matter held in the water causing the decomposition, 
and may form with it a new mineral or a number of different minerals 
occupying the place of the original one This is m part metasomatism 

The atmosphere may also act as a decomposer of minerals Through 
the agency of its oxygen it may cause their oxidation, or it may cause 
them to break up into several oxidized compounds Through the agency 
of its moisture, it may dissolve some of these secondary substances or 
it may form with them hydrated compounds The substances thus 
formed may be dissolved in water and carried off, or they may remain 
to mark the place of the mineral from which they were derived 

Water, containing traces of salts, or gases in solution are exceedingly 
active agents in effecting changes in minerals Many examples of the 
alteration of practically insoluble minerals under the influence of dilute 
solutions are known Calcite (CaCOs), for instance, when acted upon 
by a solution of magnesium chloride (MgCb) takes up magnesium and 
loses some f its calcium Monticelhte (CaMgSi04) when acted upon 
by solutions of alkaline carbonates breaks up into a magnesium silicate 
and calcium carbonate. Dilute solutions of various salts are constantly 
circulating through the earth's crust and are there effecting trans- 
formations in the minerals with which they come in contact On, or 
near, the surface the transformations are taking place more rapidly 
than elsewhere because here the solutions are aided in their decompos- 
ing action by the gases of the atmosphere 

The effect of the air in causing alteration is seen in the green coat- 
ing of malachite ((CuOH^COs) that covers surfaces of copper or of 
copper compounds exposed to its action In this particular case the 
coating is due to the action of the carbon dioxide and the moisture of 
the atmosphere. Other substances in contact with the air are coated 
with their own oxides, sulphides, etc. 

Pseudomorphs When the alteration of a mineral has proceeded 
in such a manner that the new products formed have replaced it particle 
by particle a pseudomorph results Sometimes the newly formed sub- 
stance crystallizes as a single homogeneous gram filling the entire 
space occupied by the original substance Usually, however, the alter- 



FORMATION OP MINERALS 



31 





ation begins along the surfaces of cracks or fissures in the body under- 
going alteration, or upon its exterior, thus producing the new material 
at several places contemporaneously (Fig 10) When the replace- 
ment takes place m this manner the resulting mass is a network of 
fibers of the new substance or an aggregate of grains with the outward 
form of the replaced mineral 

With respect to their method of formation chemical pseudomorphs 
may be classified as alteration 
pseudomorphs and replacement 
pseudomorphs 

Alteration Pseudomorphs. 
Pseudomorphs of this class may 
be defined as those which retain 
some or all of the constituents of 
the original minerals from which 
they were derived. 

Paramorphs. Pseudomorphs 
composed of the material of the 
pseudomorphed substance with- 
out addition or subtraction of 
any component are known as 
paramorphs. 

Paramorphism is possible only 
in the case of dimorphous bodies. 
It results from the rearrangement 
into new bodies of the particles of which the original body was com- 
posed. 

Illustrations Calcite (hexagonal CaCOs) after aragomte (ortho- 
rhombic CaCOs), orthorhombic sulphur after the monoclinic variety. 

Partial Pseudomorphs. The great majority of pseudomorphs 
retain a portion, but not all, of the material of the original mineral 
They may be formed by the addition of material to the original body, 
by the loss of material from it, or by the replacement of a portion of 
its material by new material 

Pseudomorphs formed by the addition of substance to that already 
existing are rare The substances most frequently added in the pro- 
duction of such pseudomorphs are oxygen, sulphur, the hydroxyl 
group (OH) and the carbonic acid group (CDs and COs) 

Illustrations Malachite ((CuOH^COs) after copper, aoid argentvte 
(Ag2S) after s^her. 

Pseudomorphs resulting from the loss of material are not common. 



FIG 10 Alteration of Ohvine into Ser- 
pentine The alteration is proceeding 
from the surface of the crystal and 
from surfaces of cracks that tra\erse 
it The black specks and streaks 
represent magnetite formed during the 
process (After Tschermak ) 



32 GENERAL CHEMICAL MINERALOGY 

They are caused by the abstraction of one or more of the constituents 
of a compound 

Illustration Native copper after cupnte (Cu20) 

The greater number of partial pseudomorphs are formed by the sub- 
stitution of some of the components of the original mineral by a new 
material 

Illustrations Limonite (Fe403(OH) 6 ) pseudomorphs after sidente 
(FeCOs) may be formed by the following reaction 



4 FeC0 3 + 20+3H 2 = 4C0 2 +Fe 4 3 (OH) 6 
Cerussite (PbCOs) may be formed from galena (PbS), thus 
PbS+40+Na 2 C0 3 = PbC0 3 +Na 2 S0 4 

Replacement Pseudomorphs. Often the entire substance of a 
mineral is replaced by new material, so that no trace of its original 
matter remains In this case the nature of the pseudomorphed min- 
eral can be discovered only from the form of the pseudomorph 

Illustrations Quartz (Si0 2 ) after calcite (CaCOa) and gypsum 
(CaSO 4 2H 2 0) after halite (NaCl) 

Mechanical Pseudomorphs. The processes described above as 
originating pseudomorphs are chemical, and the resulting pseudomorphs 
are sometimes designated chemical pseudomorphs There is another 
class of pseudomorphs, however, in which the substance of a crystal 
has not been replaced gradually by the pseudomorphing substance 
In this class the pseudomorphing substance simply fills a mold left by 
the solution of some preexisting crystal Thus, if a sulphur crystal 
should become encrusted with a coating of bante (BaS04) and the 
temperature should rise until the sulphur melts and escapes, there 
would be left a mold of itself constructed of bante If, now, a solution 
of calcium carbonate should penetrate the cavity and fill it with a deposit 
of calcite (CaCOs), the mass of calcite would have the shape of a crystal 
of sulphur. Pseudomorphs of this kind are known as mechanical 
pseudomorphs 

Weathering.The term weathering is applied to the sum of all the 
changes produced in minerals by the action of the atmosphere upon 
them Although nearly all minerals show some traces of weathering, 
these traces may often be detected only by the slight differences m color 
exhibited by surfaces that have been exposed for a long time to the 
action of the air when compared with fresh surfaces produced by frac- 
ture or cleavage, 



FORMATION OF MINERALS 33 

The weathering of minerals is often of great economic importance 
Veins of sulphides and a few other compounds may be oxidized where 
they outcrop on the surface Some of the decomposition products thu? 
formed may be soluble and others insoluble The insoluble products 
may remain near the surface while the soluble ones are carried down- 
ward by ground water along the course of the vein Here a reaction 
may ensue between the soluble salts and the undecomposed portion of 
the vein with the result that metallic compounds may be precipitated, 
thus enriching the original vein matter and causing it to be changed 
from a comparatively lean ore to one of great richness 

Pynte veins on the surface are often marked by accumulations of 
hmonite derived by the oxidation of the sulphide With this may be 
mixed insoluble carbonates, silicates and other salts of valuable metals 
present in the original sulphide Weathering may extend downward 
along the veins for a short distance, replacing their upper portions with 
the oxidized decomposition products This portion of a vein is often 
spoken of as the o wdized zone, and this is sometimes the richest portion 
of the vein It may be rich because less valuable substances have 
formed soluble salts and have been drained away 

Below the oxidized zone may be another zone less rich in valuable 
compounds than the oxidized zone, but much richer than the material 
below it The soluble decomposition products of the upper portion of 
the vein may percolate downward, and react with the unchanged vein 
matter, precipitating valuable metallic salts Although the original 
vein matter may contain an inconsiderable quantity of the valuable 
material, the precipitation in it of additional stores of material of the 
same kind may raise the percentage of this constituent to a point where 
it is profitable to mine it This belt of enriched ore is known as the 
zone of secondary em ichment 

The oxidized zone extends downward from the surface to a depth at 
which the atmosphere and meteoric water become exhausted of their 
oxygen a depth which varies with local conditions The zone of 
secondary enrichment extends from the bottom of the oxidized zone 
to a short distance below the level of the ground water, beyond which 
solutions will diffuse and thus be carried away from the vein. Below 
the zone of enrichment the original vein-filling may reach downward 
indefinite distances 

Since many veins exhibit the features described, it follows that the 
ore of many mines must grow poorer with depth, and that in many 
instances the richest ore is near the surface 

Some of the changes involved in weathering and secondary enrich- 



34 GENERAL CHEMICAL MINERALOGY 

ment of sulphide veins in limestone are indicated by the following reac- 
tions in the case of a vein containing pyrite (FeS 2 ), sphalerite (ZnS), 
and galena (PbS) 

(1) The first change produced at the surface may be the oxidation 
of the sulphides to sulphates 

(a) ZnS+40=ZnS04, 

(b) PbS+40=PbS04 (anglesite); 

(c) FeS 2 +70+H20=H 2 S04+FeS0 4 

(2) These may react with the limestone as follows 

(smithsomte) (gypsum) 

(a) ZnS0 4 +CaC0 3 +2H 2 0=ZnC0 3 + CaS0 4 2H 2 0, 

(cerussite) (gypsum) 

(b) PbS0 4 +CaCO 3 +2H 2 0=PbC0 3 + CaS0 4 



(3) Some of the sulphates and carbonates carried down into the un- 
altered sulphides may react with these, yielding 

Cgalena) 
(a) PbS0 4 +FeS 2 +0 2 =PbS+FeS0 4 +S0 2 , 

(galena) (sidente) 
(J) PbC0 3 +FeS 2 +0 2 =PbS + FeCOs + S0 2 ; 

(galena) 
GO PbS0 4 +ZnS = PbS+ZnS0 4 , 

(galena) (smithsonite) 
(<0 PbC0 3 +ZnS = PbS + ZnC0 3 



The PbS replacing the ZnS and deposited in the cracks in the original 
mixture of PbS, ZnS and FeS 2 increases the percentage of this compound 
in the vein and thus enriches it. 

There is also an increase in the percentage of ZnS brought about by 
the reactions between the zinc salts (ia and 20), and the pyrite, analogous 
to those between the lead salts and pyrite (30 and 36) Thus 

(sphalerite) 
ZnS0 4 +FeS 2 +0 2 = ZnS + FeS0 4 +S0 2 , 

(sphalerite) 
ZnC0 3 +FeS 2 +0 2 = ZnS + FeC0 3 +S0 2 . 



FORMATION OF MINERALS 35 

The zinc salts produced in reactions $c and $d if carried downward will 
also have the opportunity to react \\ith the pynte in the same way 

If the ZnS is deposited in fissures in the vein matter this will tend to 
enrich it with zinc 

The oxidized zone contains (smithsonite) ZnCOs, (anglesite) PbSO4, 
(cerussite) PbCOa and (limomte) Fe2(OH) 2 The ZnS0 4 , formed also 
in the oxidized zone, is so readily soluble in water that it is leached from 
the other oxidized compounds and is carried downward. 



PART II 
DESCRIPTIVE MINERALOGY 



CHAPTER III 

INTRODUCTION THE ELEMENTS 

OF the 1,000 or more distinct minerals recognized by mineralogists 
only a few (some 250) are common A few are important because they 
constitute ores, others because they are components of rock masses, 
and others simply because of their great abundance Only a few miner- 
alogists profess acquaintance with more than 500 or 600 minerals The 
majority are familiar with but 300 or 400, relying for the identification of 
the remainder upon the descriptions of them recorded in mmeralogical 
treatises 

Only the minerals commonly met with and those of economic or of 
special scientific importance are described m this book They should 
be studied with specimens before one, in order that the relation between 
the descriptions and the objects studied may be forcibly realized Min- 
eralogy cannot be studied successfully from books alone It is primarily 
a study of objects and consequently the objects should be at hand for 
inspection l 

Mineral Names. The names of the great majority of minerals end 
in the termination "ite " This is derived from the ancient Greek suffix 
"itis" which was always appended to the names of rocks to signify that 
they are rocks The first portion of the name, to which the suffix is 
added, either describes some quality or constituent possessed by the 
mineral, refers to some common use to which it has been put, indicates 
the locality from which it was first obtained, or is the name of some 
person intended to be complimented by the mineralogist who first 
described the mineral bearing it 

1 Collections of the common minerals in specimens large enough for convenient 
study may be secured at small cost from any one of the mineral dealers whose 
addresses may be found m any mmeralogical journal 



INTRODUCTION THE ELEMENTS 37 

The following examples taken from Dana illustrate some of these 
principles The mineral hematite (Fe 2 3 ) is so named because of the red 
color of its powder, chlorite (a complicated silicate), because of its green 
color, sidente (FeCOs), from the Greek word for iron, because it con- 
tains this metal, magnetite (FeaO-i) after Magnesia in Asia, goethite 
(FeO(OH)) after the poet Goethe 

The names of a few minerals end in "ine," "ane," ^ase," ^ote," etc , 
but the present tendency is to ha\ e them all end in "ite " Occasionally, 
the same mineral may have two names This may be due to the fact 
that it was discovered by two mineralogists working at the same tune 
in different places, or it may be due to the fact that the mineralogists of 
different countries prefer to follow different precedents set by the old 
mineralogists of their respective nationalities For example, the min- 
eral (Mg Fe)sSi04 is called ohmne by the Germans and by most English- 
speaking mineralogists, and peridot by the French The Germans follow 
the German mineralogist Werner, who first used the name ohvine in 
1789, while the French follow the French teacher Hauy, who proposed 
the name peridot in 1801 

ELEMENTS 

The elements that occur in nature are few in number, and these, 
with rare exceptions, do not occur in great abundance They may be 
separated into the following groups the carbon group, the sulphur 
group, the arsenic group, the silver group, and the platinum-iron 
group Some of these comprise only a single mineral, while others 
comprise six or seven Only a portion of these are described 

THE NON-METALS AND METALLOIDS 

CARBON GROUP 

The carbon group embraces several minerals of which one is dia- 
mond, another is an amorphous black substance known as schungite, 
and the other two are apparently but different forms of graphite 
The element may thereupon be regarded as tnmorphous Diamond 
and graphite are both important. 

Isometric (hextetrahedral) Hexagonal (ditngonal scalenohedral) 

Diamond Graphite 

Diamond (C) 

The diamond is usually found in distinct crystals or in irregular 
masses, varying m size from a pin's head to a robin's egg In some 
cases large individual pieces are found but they "-are exceedingly rare 



38 



DESCRIPTIVE MINERALOGY 







FIG ii Etch Figures on 
Cubic Face of Diamond 
Crystal (After Tscher- 
mak) 



The largest ever found, known as the Cullman diamond (Fig 16), 
weighed 3,024! carats or 621 grams, or i 37 Ib , 
and measured 112x64x51 mm It was cut 
into nine fine gems and a number of smaller 
ones (Fig 17) 

In composition the diamond is pure car- 
bon, but it is a form of carbon that is not 
ignited and burned at low temperatures At 
high temperatures, however, especially when 
in the presence of oxygen, it burns freely 
with the production of CC>2, and, in the case 
of opaque varieties, a little ash 

Its crystallization is isometric (hextetra- 
hedral class), and the forms on the crystals often appear to be tetra- 
hedrally hemihedral, although the 
etch figures on cubic faces suggest 
hexoctahedral symmetry (Fig n). 
Octahedrons, tetrahedrons, icositet- 
rahedrons and combinations of these 
forms are common, and in nearly all 
cases the interf acial edges are rounded 
and the crystal faces curved Some- 
times this curving is so pronounced 
that the individuals are practically 
spheres (Fig 12) Twins are com- 
mon with 0(in) as the twinning 
plane (Fig 13), 

The cleavage of diamond is per- 
fect parallel to the octahedral face. 
This is an important characteristic, as the lapidary makes use of it 
in the preparation of stones for cutting Its 
fracture is conchoidal Its specific gravity is 
3 52 and its hardness greater than that of any 
other known substance Most diamonds are 
dark and opaque, or, at most, translucent, but 
many are found that are transparent and color- 
less or nearly so Gray, brown, green, yellow, 
blue and red tinted stones are also known, and, 
with the exception of the blue and red diamonds, 
these are more common than the colorless, or 
luster of all diamonds is adamantine, and 




FIG 12 Crystal of Diamond with 
Rounded Edges and Faces (Krantz ) 




FIG 13 Octahedron of 
Diamond Twinned 
aboutO(m) 

so-called white stones 



INTRODUCTIONTHE ELEMENTS 39 

their index of refraction is very high, n=z 4024 for red rays, 2 4175 for 
yellow rays, and 2 4513 for blue ra>s In consequence of their strong 
dispersion, the reflection of light from the inner surfaces of transparent 
stones is very noticeable, causing them to sparkle brilliantly, with a 
handsome play of colors It is this latter fact and the great hardness 
of the mineral that make it the most valuable of the gems The mineral 
is a nonconductor of electricity 

Three varieties of the diamond have received distinct names in 
the trade These are 

Gem diamonds, which are the transparent stones, 

Bort, or Bortz, gray or black translucent or opaque rounded masses, 
with a rough exterior and the structure of a crystalline aggregate, and 

Carbonado, black, opaque or nearly opaque masses possessing a 
crystalline structure, but no distinct cleavage 

The only minerals with which diamond is liable to be confused 
are much softer, and, consequently, there is little difficulty in dis- 
tinguishing between them 

Syntheses Small diamonds have been made by fusing in an 
electric furnace metallic iron containing a small quantity of carbon and 
cooling the mass suddenly in a bath of molten lead They have also 
been made by heating in the electric arc pulverized carbon on a spiral 
of iron wire immersed m hydrogen under a pressure of 3,100 atmospheres 
A third method, which resulted in the production of tiny octahedrons, 
consisted in melting graphite in olivine, or in a mixture of silicates 
having the composition of the South African " blue ground," with 
the addition of a little metallic aluminium or magnesium 

Occurrence and Origin Diamonds are found (i) in clay, sand 
or gravel deposits or in the rocks formed by the consolidation of these 
substances, where they are associated with gold, platinum, topaz, 
garnet, tourmaline and with other minerals that result from the decom- 
position of granitic rocks, (2) in a basic igneous rock containing frag- 
ments of shale (a consolidated mud) and (3) small diamonds have been 
discovered in meteorites 

The manner of origin of diamonds has been a subject of contro- 
versy for many years The most popular theory ascribes the diamonds 
in igneous rocks to the solution of organic matter m the rock magmas 
and the crystallization of the carbon upon cooling Another theory 
regards the carbon as an original constituent of the magma. The 
diamonds in sand, sandstone, granite, etc , are believed to have been 
transported from their original sources and deposited in river channels 
or on beaches. 



40 DESCRIPTIVE MINERALOGY 

Localities The principal localities from which diamonds are obtained 
are the Madras Presidency in India, the Province of Mmas-Geraes in 
Brazil, the Island of Borneo, the valleys of the Vaal and Orange 
Rivers, and other places in South Africa, and the valley of the Mazarum 
River and its tributaries in British Guiana Recently diamond fields 
have been discovered in New South Wales, Australia, in the \alley of 
the Kasai River m the Belgian Kongo, in Arkansas, and in the Tula- 
meen district, British Columbia 

In the United States a few gem diamonds have been found from 
tune to time in Franklin and Rutherford counties in North Carolina, 
in the gold-bearing gravels of California, and m soils and sands in the 
states of Alabama, Virginia, Wisconsin, Indiana, Ohio, Idaho an^l 
Oregon A stone (the Dewey diamond) found near Richmond, Virginia, 
a few years ago is valued at $300 or $400 

The principal source of diamonds and carbonado in Brazil at the 
present time is Bahia, where the mineral occurs in a friable sandstone 
along river courses The output of this region has decreased so greatly 
in the last few years that although a mass of carbonado weighing 3,073 
carats (the largest mass of diamond material ever found) was obtained 
in 1895, the price of this impure diamond rose from $10 50 per carat 
m 1894 to $36 oo per carat in 1896 and $85 oo per carat for the best 
quality m 1916 

The only diamond field of prominence m the United States is that 
which has recently been exploited near Murfreesboro in Arkansas, where 
the conditions are similar to those existing in South Africa The dia- 
monds occur m a basic igneous rock (pendotite) that cuts through Scind- 
stones and quartzites The pendotite is weathered to a, soft earth or 
" ground " m which the diamonds are embedded Up to the end of 
1914 over 2,000 diamonds had been found, mostly small stones weighing 
in the aggregate 550 carats, valued at about $12,000 One, however, 
weighed 8 carats and another 7^ carats The rough unsorted stones 
are valued at $10 per carat Three stones that were cut were found 
to be worth from $60 to $175 per carat The district has not yet been 
sufficiently developed to prove its commercial value The diamonds 
in British Columbia occur in the same kind of rock as those m Arkansas 
The few that have thus far been found are too small for any practical 
use 

In former times the mines of India and Borneo were very produc- 
tive, the famous Golconda district m India for a long period furnishing 
most of the gems to commerce 

The African mines were opened in 1867 Since this time they 



mil, Ji/JjJkMIiJWTS 41 

have been practically the only producers of gem material in the world 
It is estimated that the quantity of uncut diamonds yielded by the 
mines near Kimberly alone have amounted in value to the enormous 
sum of $900,000,000 The output of the African mines in 1913 was 
sold for about $53,000,000, being over 95 per cent of the world's out- 
put of gem material Of this amount about $9,000,000 worth of stones 
were furnished by German Southwest Africa, the balance by the 
Union of South Africa The diamonds are found in a pendotite which 
occurs in the form of volcanic necks, or " pipes," cutting carbonaceous 
shales The igneous rock is much weathered to a soft blue earthy mass 
known as " blue earth " Near the surface where exposed to the action 
of the atmosphere the earth is yellow The diamonds are scattered 
through the weathered material in quantities amounting to between 
3 and 6 carat per cubic yard 

E\tr action Where the diamond occurs in sand and gravel it is ob- 
tained by washing away the lighter substances 

In South Africa and Arkansas the mineral is found in a basic volcanic 
rock which weathers rapidly on exposure to the air The weathered 
rock is mined and spread on a prepared ground to weather When suf- 
ficiently disintegrated water is added to the mass and the mud thus 
formed is allowed to pass over plates smeared with grease The dia- 
monds and some of the other materials adhere to the grease, but most 
of the valueless material is carried off by the water 

Uses Transparent diamonds constitute the most valuable gems 
in use Perfectly white stones, or those possessing decided tints of red, 
rose, green or blue are the most highly prized They are sold by 
weight, the standard being known as the carat, which, until recently, 
was equivalent to 3 168 grains or 205 milligrams At present the metric 
carat is m almost universal use This has a weight of 200 milligrams 
The price of small stones depends upon their color, brilliancy and size 
a perfectly white, brilliant, cut stone weighing one carat, being valued 
at about $175 oo As the size increases the value increases in a much 
greater ratio, the price obtained for large stones depending almost solely 
upon the caprice of the purchaser 

Nearly all the gem diamonds put upon the market are cut before 
being offered for sale The chief centers of diamond cutting are Ant- 
werp and Amsterdam in the Old World and New York in America 
The favorite cuts are the brilliant and the rose For the former only 
octahedral crystals, or those that will yield octahedrons by cleavage, 
are used, for the rose cut distorted octahedrons or twinned crystals 
In producing the "brilliant" a portion of the top of an octahedron is cut 



42 



DESCRIPTIVE MINERALOGY 



off and a small portion of the bottom On the remainder are cut three 
or four bands of facets running horizontally around the stone (see Fig 14) 
The "rose" has a flat base surmounted by a pyramidal dome consisting 
of 24 or more facets In late years the shapes into which diamonds are 
cut have been determined less by the decrees of fashion and more by the 

desire to sa\e as much ma- 
terial as possible, and, conse- 
quently, irregularly shaped cut 
diamonds are much more 
common than formerly (com- 
pare Fig 17). 

Diamonds are employed 
also as cutting tools Small 
fragments, or splinters of gem 
quality, are used for cutting 
and polishing diamonds and 




Rose 



Grona Back, or Pavilion 

Step or Trap 




Crown 



Side View 



Pavilion, or Base 

Brilliant 
FIG 14 Principal " cuts " of Diamonds 



other gems, and small crystals 
with crystal edges for cutting 
glass Small cleavage pieces 
are utilized in the manufacture of engravers' tools and writing instru- 
ments Recently diamonds with small holes of from 008 to 0006 of an 
inch drilled in them, have been employed as wne dies 

Bort is also used as a polishing and cutting material, while carbonado, 
nearly all of which comes from Brazil, is used in the manufacture of 
boring instruments Diamond drills consist of hollow cylinders of soft 
iron set at their lower edges with 6, 8 or 12 black diamonds By rapid 
revolution of this a "core" may be cut from the hardest rocks 

Some Famous Diamonds The largest diamond ever found the Cull- 
inan was picked up at the Premier Mine (Fig 15) in the Transvaal in 
January, 1905, and was presented to King Edward of England as a birth- 
day gift in 1908 (Figs 16 and 17 ) It weighed about 3,025 carats (about 
i 37 pounds) The next largest was found in June, 1893, at the Jagers- 
fontem mine It is known as the Excelsior It weighed in its natural 
state 971 carats and was 3 inches long in its greatest dimension It was 
valued at $2,000,000 It is said to have been presented by the Presi- 
dent of The Orange Free State to Pope Leo XIII The third largest 
stone is the Reitz It is a 640-carat stone found at the same mine during 
the close of 1895 This, though smaller, is said to be handsomer than the 
Excelsior The most noted diamond in the world is the Kohmoor, which 
weighed, before cutting, 186 carats It is now a brilliant of 106 carats, 
belonging to the crown of England Other famous diamonds aie the 



INTRODUCTION THE ELEMENTS 



43 




FIG 15, Premier Diamond Mines in South Africa 




p IG X 6, -The Cullman Diamond. (Natural size ) 



DESCRIPTIVE MINERALOGY 




FIG 17 Gems Cut from the Cullman Diamond (Two-lifthb nat si/c ) 

Orlov, 193 carats, the property of Russia, the Regent or Pitt diamond 
of 137 carats belonging to France, the Green diamond of Dresden, 

weighing 48 carats, and the Blue 
Hope diamond, weighing 44 carats 
The " Star of the South," found in 
Brazil, weighed 254 carats bcfoie 
cutting and 125 .iftcnvard The 
Victoria diamond from one of the 
Kimberly mines -weighed 457 carats 
\\hen found It has been cut to a 
perfect brilliant of 180 carats valued 
at $1,000,000 The Tiffany dia- 
mond (Fig 1 8) now owned in New 
York is a double brilliant of a 
golden yellow color weighing 128^ 
carats (25 702 grams) and valued at 
$100,000 When it is remembered 
that a five-carat stone is large, the 
enormous proportions of the above-named gems are better appreciated. 




FIG 1 8 -The Tiffany Diamond (Nat- 
ural size ) (Kindness of TiJJany & Co ) 



Graphite (C) 

Graphite, or plumbago, occurs principally in amorphous masses of a 
black, clayey appearance, in radiated masses, in brilliant lead black 
scales or plates, and occasionally in crystals with a rhombohedral habit 

Like diamond, graphite consists of carbon Crystals from Ceylon 
yield C=794o, Ash=is 50, Volatile matter=s 10. The mineral is 
often impure from admixture with clay, etc. 



INTRODUCTION THE ELEMENTS 45 

Crystals of the material are so rare that their symmetry is still in 
doubt Their habit is hexagonal (ditngonal scalenohedral class) 
Measurements made on the interfacial angles of crystals from Ticon- 
deroga, New York, gave a c=i i 3859 These possess a rhombo- 
hedral symmetry All crystals are tabular and nearly all are so distorted 
that the measurements of their interfacial angles cannot be depended 
upon for accuracy They apparently contain the planes R(ioTi), 

OP(IOOO), COP2(II20), and 2P2(lI2l) 

Graphite is black and earth} , or lustrous, according as it is impure 
or pure It is easily clea\ able parallel to the basal plane and the cleav- 
age laminae are flexible It is very soft, its hardness being only 1-2, 
its density about 2 25 Its luster is metallic and the mineral is opaque 
even in the thinnest flakes It is a conductor of electricity 

Graphite is infusible and noncombustible even at moderately high 
temperatures Like diamond, however, it may be burned under cer- 
tain conditions at \ ery high temperatures (65o-7oo) It is unaffected 
by the common acids and is not acted upon by the atmosphere 
When, ho\\e\er, it is subjected to the action of strong oxidizing agents, 
such as a \\arm mixture of potassium chlorate (KClOj) and fuming 
nitric acid, it changes to a }ello\\ substance kno^n as graphitic acid 
(CnKLiOj) It is thus distinguished from amorphous carbon, like 
schungite and anthracite Moreo\er, man\ forms of graphite, \\hen 
moistened with fuming nitric acid and heated, s\\ell up and send out 
worm-like processes Those \\hich do not act thus are called graphititc 
Natural graphite is of both types 

Its color, softness and infusibility serve to distinguish graphite from 
all other minerals but molybdenite (p 75) It ma\ be distinguished from 
this mineral by the fact that it contains no sulphur 

Syntheses Crystalline graphite is made on a commercial scale 
by treating anthracite coal or coke containing about 5 75 per cent of 
ash in an electric furnace It also separates \\hen molten iron con- 
taining dissolved carbon is cooled 

Occurrence and Origin Graphite occurs as thin plates and scales 
m certain igneous rocks, m gneisses, schists and limestones, as large 
scales m coarse granite dikes (pegmatite) and m crystalline limestones, 
and as amorphous masses at the contacts of igneous rocks with carbona- 
ceous rocks The mineral is also found in veins cutting sedimentary 
and metamorphic rocks Crystals are found only in limestone 

The occurrence of graphite m sedimentary and igneous rocks sug- 
gests that it may have been formed m several ways It is thought 
that the material in limestone and quartz-schist may represent carbo- 



46 DESCRIPTIVE MINERALOGY 

naceous material that was deposited with the sediments and which has 
since been carbonized by heat and pressure The material m peg- 
matite may be an original constituent of the magma that produced the 
rock, and the graphite may be the product of pneumatolytic processes , 
i c , it may have been produced by deposits from vapors that accom- 
panied the formation of the pegmatite If this be true, the mineral 
found in metamorphosed limestone and schist may be of contact origin, 
i e , it may have been produced by the migration of gases and solutions 
from igneous rocks into the mass of the surrounding sediments The 
vein deoosits probably had a similar origin, the mineral having been 
deposited mainly in cracks traversing metamorphic rocks On the 
other hand, graphite, in some instances, appears to be a direct separa- 
tion from a molten magma 

Localities The principal foreign source of supply for commercial 
graphite is the Island of Ceylon In the United States the mineral has 
been mined on the southeast side of the Adirondacks in New York, 
in Chester County, Pennsylvania, near Dillon, Montana, at several 
points in Arkansas, Georgia, Alabama and North Carolina, in Wyo- 
ming, in Baraga County, Michigan, and to a small extent in Colorado, 
Nevada, and Wisconsin It occurs also abundantly at many other 
places Its chief source in the United States is Graphite, near Lake 
George, New York 

Preparation Graphite is obtained on a commercial scale by grind- 
ing the rock containing it and floating the graphite flakes 

Uses Crude graphite, or plumbago, is used in the manufacture of 
stove and other polishes, and of black paint foi metal surfaces, for both 
of which it is especially valuable on account of its noncorrodmg propji- 
ties The purified mineral is mixed with clay and made into crucibles 
for use at high temperatures It is also ground and used m this form 
as a lubricant for heavy machinery, and is compressed into u black lead " 
centers for lead pencils 

Production The quantity of crude graphite mined m the United 
States during 1912 amounted to 2,445 tons > valued at $207,033, besides 
which there were manufactured 6,448 tons, valued at $830,193. The 
imports were 25,643 tons, valued at $709,337 

Schungjte is a black, amorphous carbon with a hardness of 3-4 
and a spgr. of i 981 It is soluble in a mixture of HNOs and KClOj 
without the production of graphitic acid. It occurs in some crystalline 
schists. 



INTRODUCTION THE ELEMENTS 



47 



SULPHUR GROUP 

Sulphur is known in at least six different forms, four of which are 
crystalline The two best known forms crystallize respectively in the 
orthorhombic (orthorhombic bipyramidal class) and the monoclimc 
(prismatic class) systems The former separates from solutions of sulphur 
in carbon bisulphide and the latter separates from molten masses 
Both the orthorhombic and the monoclimc phases are believed to be 
formed by natural processes, but the latter passes over into the former 
upon standing, so that its existence as a mineral cannot be definitely 
proven Selenium and tellurium, which are also members of the sul- 
phur group, are extremely rare Tellurium occurs in rhombohedral 
crystals and selenium in mixed crystals of doubtful character with 
sulphur and tellurium 

Sulphur (S) 

Sulphur occurs in nature as a lemon-colored powder, as spherical or 
globular masses, as stalactites and in crystals 

Chemically it is pure sulphur, or a mixture of sulphur and clay, 






FIG 19 FIG 20 

FIG 19 Sulphur Crystals with P, in (), 3?, 113 (s), P, on (), and oP, 

ooi (c) 

FIG 20 Distorted Crystal of Sulphur (Forms same as in Fig. 19 ) 

bitumen or other impurities. It sometimes contains traces of tellu- 
rium, selenium and arsenic 

Crystals of sulphur are usually well formed combinations of ortho- 
rhombic bipyramids and domes, with or without basal terminations. 
Their axial ratio = 8108 * i i 9005 The principal forms observed 
are P(in), POO(IOI), P 6(011), iP(ii3) and oP(ooi) (Figs 19 and 
20) The habit of the crystals is usually pyramidal, though crystals 
with a tabular habit are quite common 

Crystals of sulphur are yellow Their streak is light lemon yellow, 



48 DESCRIPTIVE MINERALOGY 

The mineral has a resinous luster Its hardnebs is only i 5-2, and 
density about 204 Its fracture is conchoidal and cleavage imper- 
fect It is transparent or translucent, is brittle and is a non- 
conductor of electricity Its indices of refraction for sodium light 
area = i 9579, j8a 0377, 7 = 2 2452 

Massive sulphur varies in color from yellow to yellowish brown 
greenish gray, etc , according to the character and amount of impurities 
it contains Its powder is nearly always crystalline In mass it pos- 
sesses a lighter color than the crystals or the massive sulphur 

At a temperature of 114 sulphur melts, and at 270 it ignites, 
burning with a blue flame and evolving fumes of SO 2 At about 97 
it passes over into the monoclimc phase It is insoluble in water and 
acids, but is soluble in oil of turpentine, carbon bisulphide and chlo- 
roform 

There are few minerals that are apt to be mistaken for sulphur. 
From all of them it may be distinguished by its bnttleness and by the 
fact that it melts readily and burns with a nonlummous blue flame 

Syntheses Crystals with the form of the mineral are produced by 
the evaporation of solutions of sulphur in carbon bisulphide, and also 
by sublimation from the fumes of ore roasters 

Occurrence and Origin Sulphur occurs most abundantly m regions 
of active or extinct \olcanoes, and in beds associated with limestone 
and gypsum (CaSO* 2H20) In volcanic regions it is produced by 
reactions between the gases emitted from the volcanoes, or by the reac- 
tions of these with the oxygen of the air (seep 18) The deposits in 
gypsum beds may result from reduction of the gypsum by organic 
matter. Sulphur is formed also as a decomposition product of sulphides 

In Iceland and other districts of hot springs sulphur is often deposited 
in the form of powder as the result of reactions similar to those that 
take place between the gases of volcanoes These hot springs are always 
connected with dying volcanoes, being frequently but the closing 
stages of their existence 

Localities The localities at which sulphur is known to exist are 
very numerous Those of commercial importance are Girgenti m Sicily, 
Cadiz in Spam, Japan, and in the United States, at the geysers 'of the 
Napa Valley, Sonoma County, and at Clear Lake, Lake County, 
California, at Cove Creek, Millard County, Utah, at the mines of the 
Utah Sulphur Company in Beaver County, in the same State, at 
Thermopohs, Wyoming, and at various hot springs in Nevada The 
mineral occurs also abundantly in the Yellowstone National Park, but 
cannot be placed on the market because of high transportation charges 



INTRODUCTION THE ELEMENTS 49 

Its principal occurrence m the United States is at Lake Charles in 
Calcasieu Parish, La , where it impregnates a bed of limestone at 
a depth of from 450 to 1,100 feet It occurs also abundantly in the 
coastal districts of Texas Here it is associated with gypsum 

Extraction Sulphur, when mined, is mixed with clay, earth, rock and 
other impurities Until recently it was purified by piling in heaps and 
igniting A portion of the sulphur burned and melted the balance, 
which flowed off and was caught A purer product is ob tamed by dis- 
tillation "Flowers of Sulphur" are made in this way At present 
much of the sulphur is extracted by treating the impregnated rock m 
retorts with steam under a pressure of 60 pounds and at a temperature 
of 144 C The sulphur melts and flows to the bottom of the retorts 
from which it is drawn off 

In Louisiana and Texas, superheated steam is forced downward into 
the sulphur-impregnated rocks. This melts the sulphur, which con- 
stitutes about 70 per cent of the rock mass The melted sulphur is 
forced to the surface and caught in wooden bins The crude material 
has a guaranteed content of over 99! per cent sulphur 

Uses Sulphur, or brimstone, is used m the manufacture of some 
kinds of matches, m making gunpowder, and m vulcanizing rubber 
to increase its strength and elasticity It is used extensively in the 
manufacture of sulphuric acid, but is rapidly giving way to pynte 
for this purpose It is also utilized for bleaching straw, in the man- 
ufacture of certain pigments, among \\hich is vermilion, and in the 
preparation of certain medicinal compounds 

Production Most of the domestic product is at present from the 
Calcasieu Pansh, La , where about 300,000 tons are mined annually. 
New mines have been opened near Thermopolis in Wyoming, in Bra- 
zona County, Texas, and at Sulphur Springs, Ne\ada. The total 
amount of the mineral mined in 1912 was 303,472 tons, valued at $5,256,- 
422 Besides, there were imported about 29,927 tons valued at $583,974, 
most of which came from Japan Sicily is the largest producer of the 
mineral, extracting about 400,000 tons annually. 

ARSENIC GROUP 

The arsenic group comprehends metallic arsenic, antimony, bismuth 
and (according to some mineralogists), tellurium, besides compounds 
of these metals with each other They all crystallize in the rhombo- 
hedral division of the hexagonal system (ditrigonal scalenohedral class). 
The only members of the group that are at all common are arsenic and 
antimony 



50 DESCRIPTIVE MINERALOGY 

Arsenic (As) 

Arsenic is rarely found in crystals It usually occurs massive or in 
botryoidal or globular forms 

Specimens of the mineral are rarely pure They usually contain 
some antimony, and traces of iron, silver, bismuth, and other metals 

The crystals are cubical in habit, with an axial ratio of i . i 4025 
The principal forms observed are oR(oooi), R(ioTi), JR(ioT4), 
|R(oil2) and ^(0332) Twins are rare, with -|R(oil2) the 
twinning plane 

Arsenic is lead-gray or tin-white on fresh fractures, and dull gray or 
nearly black on surfaces that have been exposed for some time to the 
atmosphere 

Crystals cleave readily parallel to the base The fracture of massive 
pieces is uneven The mineral is brittle Its hardness is 3 5 and its 
density 5 6-5 7 Its streak is tin-white tarnishing soon to dark gray 
It is an electrical conductor 

Arsenic may easily be distinguished from nearly all other minerals, 
except antimony and some of the rarer metals, by the color of its fresh 
surfaces From these, with the exception of antimony, it is also readily 
distinguished by its action on charcoal before the blowpipe, when it 
volatilizes completely without fusing, at the same time tmgeing the 
flame blue and giving rise to dense white fumes of As20s, which coat the 
charcoal The fumes of arsenic possess a very disagreeable and oppres- 
sive odor, while those of antimony have no distinct odor 

Syntheses Arsenic has been obtained in crystals by subliming 
arsenic compounds protected from the air It has also been obtained m 
the wet way by heating realgar (As2Sa) with sodium bicarbonate at 
300 C 

Occurrence and Origin Arsenic often accompanies ores of antimony, 
silver, lead and other metals in veins in crystalline rocks, especially in 
their upper portions, where it was formed by reduction from its com- 
pounds 

Locahties The silver mines at Freiberg, and other places m Saxony 
afford native arsenic in some quantity It is found also in the Harz, at 
Zmeov in Siberia, in the silver mines of Chile and elsewhere. 

Within the boundaries of the United States arsenic occurs only in 
small quantity at Haverhill, N H , at Greenwood, Me , and at a silver 
and gold mine near Leadville, Colo 

Uses Arsenic is used only in the forms of its compounds The 
native metal occurs too sparingly to be of commercial importance. 



INTRODUCTION THE ELEMENTS 51 

Most of the arsenic compounds used in commerce are obtained from 
smelter fumes produced by smelting arsenical copper and gold ores 

Antimony (Sb) 

Antimony is more common than arsenic, which it resembles in many 
respects It is generally found in lamellar, radial and botryoidal masses, 
though rhombohedral crystals are known 

Most antimony contains arsenic and traces of silver, lead, iron and 
other metals 

Its crystals are rhombohedral or tabular in habit, and have an axial 
ratio of a : c=i . i 3236 The forms observed on them are the same 
as those on arsenic with the addition of ocP2(ii2o), and several 
rhombohedrons Twinning is often repeated The cleavage is perfect 
parallel to oP(oooi) 

Antimony exhibits brilliant cleavage surfaces with a tin-white color 
On exposed surfaces the color is dark gray The mineral differs from 
arsenic in its greater density which is 6 65-6 72, and in the fact that it 
melts (at 629) before volatilizing Its fumes, moreover, are devoid of 
the garlic odor of arsenic fumes 

Syntheses Crystals of antimony are often obtained from the flues of 
furnaces in which antimomal lead is treated. They have also been 
made by the reduction of antimony compounds by hydrogen at a high 
temperature 

Occurrence and Localities Antimony occurs in lamellar concretions 
in limestone near Sala, Sweden, and at nearly all of the arsenic localities 
mentioned above, especially in veins containing stibnite (Sb2Ss) or silver 
ores It is found also in fairly large quantities in veins near Fredencton, 
York County, New Brunswick, in California and elsewhere 

Uses Although the metal antimony is of considerable importance 
from an economic point of view, being used largely in alloys, the native 
mineral, on account of its rarity, enters little into commerce Some of 
the antimony used m the arts is produced from its sulphide, stibnite 
(see p 72) Most of the metal, however, is obtained in the form of a 
lead-antimony alloy in the smelting of lead ores and the refining of pig 
lead 

Bismuth (Bi) is usually in foliated, granular or arborescent forms, 
and very rarely in rhombohedral crystals, with a . c=i ' i 3036 It is 
silver-white with a reddish tinge, is opaque and metallic Its streak is 
white, its hardness 2-2 5 and density 98 It fuses at 271. On charcoal 
it volatilizes and gives a yellow coating It dissolves in HNOs When 



52 DESCRIPTIVE MINERALOGY 

this solution is diluted a white precipitate results The mineral occurs 
in veins with ores of silver, cobalt, lead and zinc It is of no commercial 
importance Most of the metal is obtained in the refining of lead In 1913 
the United States produced 185,000 Ibs and Bolivia about 606,000 Ibs 

Tellurium (Te) usually occurs in prismatic crystals with a tin-white 
color and in finely granular masses in veins of gold and silver ores, 
especially sulphides and tellundes Its hardness is 2 and density 6 2 
Before the blowpipe it fuses, colors the flame green, coats the charcoal 
with a white sublimate bordered by led, and yields white fumes 

The mineral tellurium is of little value as a source of the metal 
Most of that used in the arts is obtained as a by-product in the elec- 
trolytic refining of copper made from ores containing tellundes and 
from the flue dust of acid chambers and smelting furnaces The United 
States, in 1913, produced about 10,000 Ibs of tellurium and selenium, 
valued at $3^,000 

THE METALS 

The metallic elements occur as minerals m comparatively small quan- 
tity, most of the metals used in the industries being obtained from their 
compounds Iron, the most common of all the metals used in com- 
merce, is rare as a mineral, as are also lead and tin Silver, copper, gold 
and platinum are sufficiently important to be included in our list for 
study Gold and platinum are known almost exclusively in the metallic 
state A large portion of the copper produced in this country is also 
native, and some of the silver 

Silver, copper, lead, gold, mercury and the alloys of gold and mer- 
cury crystallize in distinct crystals belonging to the isometric system 
(hexoctohedral class) Platinum, as usually found, is in small plates 
and grains Crystals, however, have been described and they, too, are 
isometric Platinum and iron are separated from the other metals and, 
together with the rare alloys of platinum with indium and osmium, are 
placed in a distinct group which is dimorphous The reason for this is 
that platinum, although isometric in crystallization, often contains 
notable traces of indium, which in its alloy with osmium is hexagonal 
(rhombohedral) Indium, thus, is dimorphous, hence platinum which 
forms crystals with it and is, therefore, isomorphous with it, must also 
be regarded as dimorphous The various platinum metals thus com- 
pnse an isodimorphous group Iron is placed in the same group because 
it is so frequently alloyed with platinum The metals are, therefore, 
divisible into two groups, one of which comprises the metals named at 



INTRODUCTION THE ELEMENTS 



53 



the beginning of this paragraph and the other consists of the rare metals, 
palladium, platinum, indium, osmium, iron and their alloys The 
metal tin, which is tetragonal m its native condition, constitutes a third 
group, but since it is extremely rare it will not be referred to again 

GOLD GROUP 

This group embraces the native metals, copper, siker, gold, gold- 
amalgam (Au Hg), siher-amalgam (Ag Hg), mercury, and leal All 
crystallize in the isometric system (hexoctahedral class), and all form 
twins, with 0(in) the twinning plane Copper, silver and gold are 
the most important 

Copper (Cu) 

Most of the copper of commerce is obtained from one or the other of 
its sulphides A large portion, however, is 
found native This occurs m tiny grams and 
flakes, in groups of crystals and in large 
masses of irregular shapes 

In spite of its softness copper is better 
crystallized than either gold or silver It is 
true that its crystals are usually flattened and 
otherwise distorted, but, nevertheless, planes 

can very frequently be detected upon them 

rr.i - i * , -, >v / \ FIG 2i. Copper Crystal 

The principal forms observed are oo O oo (100), ^^ M Q *^ * , 

oo O(no), 0(ni), and various tetrahexahedra 20 & 1 2 io' (h). 

and icositetrahedra. (Figs. 21 and 22 ) Some- 
times the crystals are sim- 
ple, in other cases they are 
twinned parallel to O 
Often they are skeleton 
crystals Groups of crys- 
tals are very common 
These possess the arbo- 
rescent forms so frequently 
seen in specimens from 
Keweenaw Point in Mich- 
igan, or are groupings of 
simple forms extended in 
the direction of the cubic 





FIG. 22. Crystal of Copper from Keweenaw Point, 
Mich , with wO(iio) and 202(211) 



axes. 



Cbpper is very ductile and very malleable Its hardness is only 



54 DESCRIPTIVE MINERALOGY 

2 5-3 and its density about 88 It possesses no cleavage, and its frac- 
ture, like that of the other metals, is hackly In color it is copper-red 
by reflected light, often tarnishing to a darker shade of red In very 
thin plates it is translucent with a green color The metal fuses at 
1083 and easily dissolves in acids It is an excellent conductor of elec- 
tricity 

Its most characteristic chemical reaction is its solubility in nitric 
acid with the evolution of brownish red fumes of nitrous oxide gas 

Copper may easily be distinguished from all other substances except 
gold and a few alloys by its malleability and color It is distinguished 
from gold by the color of its borax bead and by its solubility in nitric 
acid with the production of a blue solution which takes on an intense 
azure color when treated with an excess of ammonia From the alloys 
that resemble it, copper may be distinguished by its greater softness and 
the fact that it yields no coatings when heated on charcoal, while at the 
same time its solution in nitric acid yields the reaction described above 

Syntheses Copper crystals separate upon cooling solutions of the 
metal in silicate magmas and upon the electrolysis of the aqueous solu- 
tions of its salts 

Occurrence The principal modes of occurrence of the metal are, (i) 
as fine particles disseminated through sandstones and slates, (2) as solid 
masses filling the spaces between the pebbles and boulders making up 
the rock known as conglomerate, (3) in the cavities in old volcanic lavas, 
known as amygdaloid, (4) as crystals or groups of crystals imbedded m 
the calcite of veins, (5) in quartz veins cutting old igneous rocks or 
schists, and (6) associated with the carbonates, malachite and azurite, 
and with its different sulphur compounds, in the weathered zone of 
many veins of copper ores 

The copper that occurs in the upper portions of veins of copper 
sulphides is plainly of secondary origin That which occurs in conglom- 
erates and other fragmental rocks and in amygdaloids was evidently 
deposited by water, but whether by ascending magmatic water or by 
descending meteoric water is a matter of doubt 

Localities Native copper is found in Cornwall, England, in Nassau, 
Germany, in Bolivia, Peru, Chile and other South American countries, 
in the Appalachian region of the United States and in the Lake Superior 
region, both on the Canadian and the American sides 

The most important district in the world producing native copper is 
on Keweenaw Point, in Michigan The mineral occurs mainly in a bed 
of conglomerate of which it constitutes from i to 3 per cent, though it is 
found abundantly also in sandstone and in the amygdaloidal cavities 



INTRODUCTION THE ELEMENTS 55 

of lavas associated with the conglomerates Veins of caicite, through 
which groups of bright copper en stals are scattered are also very plentiful 
in many parts of the district The copper is nearh always mixed with 
silver in visible grains and patches 

Extraction and Refining The rock containing the native metal is 
crushed and the metal is separated from the useless material by wash- 
ing The concentrates, consisting of the crushed metal mixed with 
particles of rock and other impurities are then refined by smelting 
methods or by electrolysis 

Uses The uses of copper are so many that all of even the important 
uses cannot be mentioned in this place Both as a metal and in the form 
of its alloys it has been employed for utensils and war implements since 
the earliest times In recent times one of its principal uses has been for 
the making of telegraph, telephone and trolley wires It is employed 
extensively in electroplating by all the great newspapers and publishers, 
and is an important constituent of the valuable alloys brass, bronze, 
bell metal and German silver Its compound, blue vitriol (copper sul- 
phate), is used in galvanic batteries, and its compounds with arsenic 
are utilized as pigments 

Production The world's production of copper amounted to 1,126,- 
ooo tons in 1912, but a large portion of this was obtained from its car- 
bonates and sulphides The quantity obtained from the native metal is 
unknown The contribution of the United States to this total was 
about 621,000 tons, valued at about $206,382,500, of which 115,000 tons 
was native copper from the Lake Superior region The largest single 
mass ever found in the Lake Superior region weighed 420 tons 

Silver (Ag) 

Silver is usually found in irregular masses, in flat scales, in fibrous 
dusters, and in crystal groups with arborescent or acicular forms 
Sometimes the crystals are well developed, more frequently they ex- 
hibit only a few distinct faces, but in most cases they are so distorted 
that it is difficult to make out their planes 

Pure silver is unknown The mineral as it is usually obtained con- 
tains traces of gold, copper, and often some of the rarer metals, depend- 
ing upon its associations. 

Ideally developed silver crystals are rare They usually show 
ooOoo(ioo), 006(110), 0(in) various tetrahexahedrons and other 
more complicated forms The majority of the crystals are distorted by 
curved faces and rounded edges, and many of them by flattening or 



56 DESCRIPTIVE MINERALOGY 

elongation The arborescent groups usually branch at angles of 60, 
one of the characteristic angles for groups of isometric crystals Twins 
are quite common, with O(iii) the twinning plane 

Silver is a white, metallic mineral when its surfaces arc clean and 
fresh As it usually occurs it possesses a gray, black or bluish black 
tarnish which is due to the action of the atmosphere or of solutions 
The tarnish is commonly either the o\ide or the sulphide of silvci 

The mineral has no cleavage Its fracture is hackly II is soft 
(hardness 2-3), malleable and ductile, and is an excellent conductor 
of heat and electricity Its density is about 10 5, varying slightly 
with the character and abundance of its impurities It fuses at 
960 

It is readily soluble in nitric acid forming a solution from which 
a white curdy precipitate of silver chloride is thrown down on the 
addition of any chloride This precipitate is easily distinguished from 
the corresponding lead chloride by its insolubility in hot water 

Synthesis Crystals bounded by 0(in) and o oo (100) have been 
made by the reduction of silver sulphate solutions, with sulphurous 
acid 

Occurrence Native silver is found in veins with calcite (CaCOO? 
quartz (8102), and other gangues traversing crystalline rocks, like 
granite and various lavas, and also in veins cutting conglomerates 
and other rocks formed from pebbles and sands It is also disseminated 
in small particles through these rocks It occurs invisibly disseminated 
in small quantities through many minerals, particularly sulphides, 
and visibly intermingled with native copper It is abundant in the upper 
weathered zones of many veins of silver-bearing ores, and m the zones 
of secondary enrichment in the same veins It also occurs in small 
quantity m placers In general, its origin is similar to that of gold 
(see p 59) 

Localities The localities in which silver is found are too numerous 
to mention Andreasberg in the Harz has produced many fine crys- 
tallized specimens The principal deposits now worked are at Cobalt 
in Canada, in Peru, in Idaho, at Butte, Montana, in Arizona and at 
many places m Colorado On Keweenaw Point, in Michigan, fine 
crystals have been found in the calcite veins cutting the copper-bearing 
rocks, and masses of small size in the native copper so abundant in the 
district Indeed some of the copper is so rich in silver that the ore 
was in early times mined almost exclusively for its silver content At 
present the silver is recovered from the copper in the refining process 
At Cobalt the mineral occurs m well defined veins one inch to one foot 



INTRODUCTION THE ELEMENTS 57 

or more in width, cutting a series of slightly inclined pre-Cambnan 
beds of fragmental and igneous rocks The \eins contain native silver, 
sulphides and arsenides of cobalt, nickel, iron and copper, caicite and a 
little quartz Many of the veins are so rich (Fig 23) that Cobalt has 
become one of the most important camps producing native silver in 
the world. 

Extraction and Refining Silver is obtained from placers in small 
quantity by the methods made use of in obtaining gold (see p 6i\ 
i e , by hydraulic mining When it occurs in quartz veins or m complex 
ores such as constitute the oxidized portion of ore-bodies, the mass 
may be crushed and then treated with quicksilver, which amalgamates 
with the native silver and gold, forming an alloy. Such ores are known 




FIG. 23 Plate of Silver from Confagas Mine Cobalt Dimensions 32X14X1 
ins Weight 37 Ibs. (Photo by C W. Knight ) 

as free milling The silver is freed from the gold and other metals by 
a refining process. It is separated from native copper by electrolytic 
methods. 

U ses Silver is used in the arts to a very large extent Jewelry, 
ornaments, tableware and other domestic utensils, chemical apparatus 
and parts of many physical instruments are made of it It is used also 
in the production of mirrors and in the manufacture of certain compounds 
used in surgery and in photography Its alloy with copper forms the 
staple coinage of China, Mexico and most of the South American coun- 
tries, and the subsidiary (or small) coinage of most countries In 
the United States it is used in the coinage of silver dollars and of frac- 
tions of the dollar as small as the dime. The silver corns of the United 
States are nine-tenths silver and one-tenth copper, the latter metal being 
added to give hardness English corns contain i2| parts silver to one 



58 DESCRIPTIVE MINERALOGY 

part of copper In 1912 the world's coinage of silver consumed 161,- 
763,415 02 , with a value after coinage of $171,293,000 

Production The total production of silver in the United States 
during 1912 was over 63,766,000 oz , valued at over $39,197,000, of 
which about $100,000 worth came from placers and $325,000 worth 
from the copper mines of Michigan The balance was obtained by 
smelting silver compounds and in the refining of gold, lead, copper and 
zinc ores The world's production of silver during 1912 was 224,488,- 
ooo oz , valued at over $136,937,000, but most of this was obtained 
from the compounds of silver and not from the native metal The 
proportion obtained from the mineral is not definitely known, but the 
production of Canada was more than 30,243,000 oz , valued at 
$17,672,000 and nearly all of this came from Cobalt, where the ore is 
native silver 

Gold (Au) 

A large portion of the gold of the world has been obtained m the 
form of native metal The greater portion of the metal is so very finely 
disseminated through other minerals that no sign of its presence can be 
detected even with high powers of the microscope Although present 
in such minute quantities it is very widely spread, many rocks con- 
taining it jn appreciable quantities Its visible grains, as usually found, 
are little rounded particles or thin plates or 
scales mixed with sand or gravel, or tiny 
irregular masses scattered through white vem- 
quartz 

Native gold rarely occurs in well formed 
crystals The metal is so soft that its crystals 
are battered and distorted by very slight 
pressure. Occasionally well developed crys- 
tals, bounded by octahedral, dodecahedral 
FIG 24 -Octahedral Skele- and compllcated ico sitetrahcdral and tetra- 
ton Crystal of Gold with ,_,,,- , t 

Etched Faces hexahedral faces are met with, but usually 

the crystals are elongated or flattened Skele- 
ton crystals (Fig. 24) and groups of crystals are more frequently found 
than are simple crystals. Twins are common, with O(iii) the twin- 
ning plane 

As found in nature, gold is frequently alloyed with silver and it 
often contains traces of iron and copper and sometimes small quanti- 
ties of the rarer metals 

Gold containing but a trace of silver up to 1 6 per cent of this metal 




INTRODUCTION THE ELEMENTS 59 

is known simply as gold When the percentage of silver present is 
larger it is said to be argentiferous When the percentage reaches 
20 per cent or above the alloy is called clectru ,: Palladium, rhodium 
and bismuth gold are alloys of the last-named metal roth the rare metals 
palladium or rhodium or with the more common bismath 

The color of the different varieties of the mineral varies from pinkish 
silver-white to almost copper-red Pure gold is golden yellow With 
increase cf silver it becomes lighter in color and T\ith increase in copper, 
darker The rich red-yellow ot much of the gold used in the arts is due 
to the admixture ot copper In very thin plates or lea\ es ( ooi mm ) 
gold is translucent \\ith a blue or green tint 

Gold is soft, malleable and ductile Its luster is, of course, metallic 
and its streak, yellow When pure its density is 1943, its hardness 
between 2 and 3, and its fusing point 1062 The metal is insoluble in 
most acids, but it is readily dissolved in a mixture of nitric and hydro- 
chloric acids (aqua regia) It is not acted upon by water or the atmos- 
phere Its negative properties distinguish it from the other substances 
-which it resembles in appearance It is a good conductor of electricity. 

Syntheses Crystals of gold have been obtained by heating a solu- 
tion of AuCls in amyl alcohol, and by treating an acid solution of the 
same compound with formaldehyde 

Occurrence Native gold is tound in the quartz of veins cutting 
through granite and schistose rocks, or in the gravels and sands of rivers 
whose channels cut through these, and in the sands of beaches bordering 
gold-producing districts It is sometimes found in the compacted 
gravels of old river beds, in a rock known as conglomerate, and in sand- 
stones It is also present in small quantities in many volcanic rocks, 
and is disseminated through pyrite (FeS2) and some other sulphur com- 
pounds and their oxidation products 

The gold in quartz veins occurs as grains and scales scattered through 
quartz irregularly, often in such small particles as to be invisible to the 
naked eye, or as aggregates of crystals in cavities in the quartz Pyrite 
is nearly always associated with the gold. On surfaces exposed to the 
weather the pyrite rusts out and stains the quartz, leaving it cavernous 
or cellular 

Most of the world's supply of gold has come from placers. These 
are accumulations of sand or gravel in the beds of old river courses 
The sands of modern streams often contain considerable quantities of 
gold Many of the older streams were much larger than the modern 
ones draining the same regions and, consequently, their beds contain 
more gold This was originally brought down from the mountains or 



60 DESCRIPTIVE MINERALOGY 

highlands in which the streams had their sources The sands and 
gravels were rolled along the streams' bottoms and their greater portion 
was swept away by the currents into the lowlands The gold, however, 
being much heavier than the sands and pebble grains, merely rolled 
along the bottoms, dropping here and there into depressions from which 
it could not be removed As the streams contracted in volume the gold 
grains were covered by detritus, or perhaps a lava stream flowing along 
the old river channel buried them These buried river channels with 
their stores of sands, gravels and gold constitute the placers With the 
gold are often associated zircon crystals, garnets, diamonds, topazes 
and other gem minerals Alluvial gold is usually in flattened scales or 
in aggregates of scales forming nuggets Some of the nuggets are so 
large, 190 pounds or more in weight, that it is thought they may have 
been formed by some process of cementation after they were transported 
to their present positions 

The gold-quartz veins are usually closely associated with igneous 
rocks, but the veins themselves may cut through sedimentary beds or 
crystalline schists The veins are supposed to have been filled from 
below by ascending solutions Metallic gold is also present m the oxi- 
dized zones of many veins of gold-bearing sulphides and m the zones of 
secondary enrichment At the surface the iron sulphides are oxidized 
into sulphates, leaving part of the gold m the metallic state and dissolv- 
ing another part which is carried downward and precipitated 

Principal Localities Vein gold occurs m greater or less quantity in 
all districts of crystalline rocks It has been obtained m large quantity 
along the eastern flanks of the Ural Mountains, this having been the 
most productive region in the world between the years 1819 and 1849 
It has been obtained also from the Altai Mountains in Siberia, from the 
mountains m southeastern Brazil, from the highlands of many of the 
Central and South American countries, and from the western portion of 
the United States, more particularly from the western slopes of the Sierra 
Nevada Mountains and the higher portions of the Rocky Mountains 
In recent years auriferous quartz veins have been worked at various 
points m Alaska, at Porcupine, Ontario, and other points in Canada 

The great placer mines of the world are in California, Australia and 
Alaska In Australia the principal gold mines are situated m the streams 
rising in the mountains of New South Wales and their extension into 
Victoria The valleys of 'the Yukon and other rivers m Alaska have 
lately attracted much attention, and in the past few years the beach 
sands off Nome have yielded much of the metal 

The most important production at present is from South Africa 



INTRODUCTION THE ELEMENTS 61 

where the metal occurs in an old conglomerate In the opinion of some 
geologists this is an old beach deposit, in the opinion of others the gold 
was introduced into the conglomerate long after it had consolidated 

The sands of many streams in Europe and in the eastern United 
States have for many years been "panned" or cashed for gold The 
South Atlantic States, before the discovery of gold m California, in 
1849, yielded annually about a million dollars' worth of the precious 
metal All of it was obtained by working the gra\ els and sands of small 
rivers and rivulets Many of these streams have been worked o\er 
several times at a profit and the mining continues to the present day 
Small quantities of gold have also been obtained from streams in Maine, 
New Hampshire, Maryland and other Atlantic coast states 

Extraction and Refining Gold is extracted from alluvial sands 
and from placers by washing in pans or troughs The sand, gravel 
and foreign particles are carried away by currents of water and 
the gold settles down with other heavy minerals to the bottom of the 
shallow pans used in hand washing, or into compartments prepared for 
it in troughs when the processes are on a larger scale It is after- 
ward collected by shaking it with mercury or, quicksilver, m \\hich it 
dissolves The quicksilver is finally driven off by heat and the gold 
left behind Auriferous beach sands and many lake, swamp and mer 
sands are dredged, and the sand thus raised is treated by similar methods 
Sands containing as low as 15 cents' worth of metal per cubic yard can 
be worked profitably under f a\ orable conditions 

Where the gold occurs free (not disseminated through sulphides) 
in quartz the rock is crushed to a fine pulp -with -water and the mixture 
allowed to flow over copper plates coated \uth quicksilver The gold 
unites with the quicksilver and forms an alloy from which the mercury 
is driven off by heat The process of forming allo}s of silver or gold 
with mercury is known as amalgamation 

When the gold is disseminated through sulphides, these are concen- 
trated, i e , freed from the gangue material by washing and then 
roasted This liberates the gold which is collected by amalgamation, 
or is dissolved by chlorine or cyanide solutions and then precipitated 

Uses Gold, like silver, is used in the manufacture of jewelry and or- 
naments, in the manufacture of gold leaf for gilding and in the produc- 
tion of valuable pigments such as the "purple of Cassms " It also con- 
stitutes the principle medium for coinage in nearly all of the most 
important countries of the world The gold coins of the United States 
contain 900 parts gold in 1,000. Those of Great Britain contain 916 66 
parts, the remaining parts consisting of copper and silver The total 



62 DESCRIPTIVE MINERALOGY 

gold coinage of the United States mints from the time of their organi- 
zation to the end of the year 1912 amounted to $2,765,900,000 The 
gold coined in the world's mints in 1912 amounted m value to $360,- 
671,382, and that consumed in arts and industries to $174,100,000 
Jewelers estimate the fineness of gold in carats, 24-carat gold being pure 
Eighteen-carat gold is gold containing 18 parts of pure gold and 6 parts 
of some less valuable metal, usually copper The copper is added to 
increase the hardness of the metal and to give it a darker color The 
gold used most in jewelry is 14 or 12 carats fine 

Production The total value of the gold product of the United 
States during 1912 was $93,451,000 Of this the following states and 
territories were the largest producers 

Alaska $17,198,000 Nevada $13,576,000 

California 20,008,000 South Dakota 7,823,000 

Colorado 18,741,000 Utah 4,312,000 

Of the total product, placers gelded gold valued at $23,019,633, and 
quaitz veins, metal valued at $62,112,000 The balance of the gold was 
obtained from ores mined mainly for other metals, and in these it is 
probably not in the metallic state Moreover, some of the ore in quartz 
veins is a gold telluride, but by far the greater portion of the product 
from the quartz veins and placers was furnished by the native metal 

The world's yield of the precious metal in 1912 was valued at $466,- 
136,100 The principal producing countries and the value of the gold 
produced by each were 

South Africa $211,850,600 Mexico $24,450,000 

United States 93,45 1,500 India 11,055,700 

Australasia 54,509,400 Canada 12,648,800 

Russia 22,199,000 Japan 4,467,000 

Lead occurs very rarely as octahedral or dodecahedral crystals, 
in thin plates and as small nodular masses in districts containing man- 
ganese and lead ores and also in a few placers It usually contains 
small quantities of silver and antimony The native metal ha 1 } the 
same properties as the commercial metal Its hardness 13 i 5 and 
density 113 It melts at about 33 5 

The mineral is of no commercial importance The metal is obtained 
from galena and other lead compounds 

Mercury occurs as small liquid globules in veins of cinnabar (HgS) 
from which it has probably been reduced by organic substances, and ift 



INTRODUCTION THE ELEMENTS 63 

the rocks traversed by these veins The native metal possesses the 
same properties as the commercial metal It solidifies at 39, when 
it crystallizes in octahedrons ha\mg a cubic cleavage Its density is 
13 6 Its boiling-point is 350 

The commercial metal is obtained from cinnabar (p 98). 

Amalgam (Ag Hg) is found in dodecahedral crystals in a few places, 
associated with mercury and silver ores It occurs also as embedded 
grams, m dense masses and as coatings on other minerals It is silver- 
white and opaque and gives a distinct silver streak when rubbed on 
copper Its hardness is about 3 and its density 13 9 When heated 
in the closed tube it yields a sublimate of mercury and a residue of 
silver On charcoal the mercury volatilizes, leaving a silver globule, 
soluble in nitric acid 

PLATINUM-IRON GROUP 

The platinum-iron group of minerals may be divided into the plati- 
num and the iron subgroups The latter compnses only iron and nickel- 
it on, both of which are extremely rare, and the former, the metals 
platinum, indium, osmium, ruthenium, rhodium, and palladium The 
platinum metals probably constitute an isodimorphous group since 
they occur together in alloys, some of which are isometric and others 
hexagonal (rhombohedral) Platinum is the only member of the group 
of economic importance. 

Platinum (Pt) 

Platinum occurs but rarely in crystals It is almost universally 
found as granular plates associated with gold in the sands of streams 
and rivers, and rarely as tiny grains or flakes in certain very basic 
igneous rocks 

As found in nature the metal always contains iron, indium, rhodium, 
palladium and often other metals. A specimen from California yielded: 

Pt Au Fe Ir ^Rh Pd Cu IrOs Sand Total 
85 50 80 6 75 i 05 i oo 60 i 40 i 10 2 95 101 15 

Though the metal occurs usually in grains and plates, nevertheless 
its crystals are sometimes found. On them cubic faces are the most 
prominent ones, though the octahedrons, the dodecahedrons and 
tetrahexahedrons have also been identified Like the crystals of silver 
and gold, those of platinum are frequently distorted. 



64 DESCRIPTIVE MINERALOGY 

The color of platinum is a little more gray than that of silver Its 
streak is also gray Its hardness is 4-4 5 and density 14 to 19 Pure 
platinum has a density of 21 5 It is malleable and ductile, a good 
conductor of electricity, and it is infusible before the blowpipe except 
in very fine wire It is not dissoh ed by any single acid, though soluble, 
like gold, in aqua regia Its melting temperature is 1755 

Syntheses Crystals have been obtained by cooling siliceous mag- 
mas containing the metal, and by dissolving the metal in saltpelei and 
cooling the mixture 

Occurrence Platinum is found in the sands of rivers or beaches 
and in placer deposits in which it occurs in flattened scales or in 
small grains Nuggets of considerable size are sometimes met with, 
the largest known weighing about iSf kilos It is present also in 
small quantity in certain very basic igneous rocks, like pendotite 

Localities It occurs m nearly all auriferous placer districts and 
in small quantities in the sands of many rivers, among them the Ivalo 
in Lapland, the Rhine, the rivers of British Columbia, and of the Pacific 
States It is more abundant in the Natoos Mountains in Borneo, on 
the east flanks of the Ural Mountains in Siberia, in the placer of an 
old river in New South Wales, Australia, and the sands of rivers of 
the Pacific side of Colombia It is nearly always associated with 
chromite (p 200) A recent discovery which may prove to be of con- 
siderable importance is near Goodsprmgs, Nev , where platinum is in 
the free state associated with gold in a siliceous oie 

The native metal is probably an original constituent of some pen- 
dotites (basic igneous rocks) Its presence m placers is due to the 
disintegration of these rocks by atmospheric agencies 

Extraction and Refimng The metal is separated from the sand 
with which it is mixed by washing and hand picking The metallic 
powder is then refined by chemical methods 

Uses On account of its infusibihty and its power to resist the coi- 
rosion of most chemicals the metal is used extensively for ciuciblcs 
and other apparatus necessary to the work of the chemist It is also 
used by dentists and by the manufacturers of incandescent electric 
lamps It is an important metal in the manufactuie of physical and 
certain surgical instruments, and was formerly used by Russia for coin- 
age The most important use of the metal in the industries is in the 
manufacture of sulphuric acid Sulphur dioxide (SCb) and steam when 
mixed and passed over the finely divided metal unite and foim HjSOi 
More than half of the acid made at present as manufactured by this 
process 



INTRODUCTION THE ELEMENTS 



65 



Production Most of the platinum of the world is obtained from 
placers in the Urals in Russia A small quantity is washed from the 
sands of gold placers in Colombia, Oregon and California, and an even 
smaller quantity is obtained during the refining of copper from the ores 
of certam mines The total production of the world in 1912 was 
314,751 oz The output for Russia m this year was about 300,000 oz , 
of Colombia about 12,000 oz , and of the United States 721 oz (equiv- 
alent to 505 02 of the refined metal, valued at $22,750) In addition, 
about 1,300 oz were obtained m the refining of copper bullion imported 
from Sudbury, Ont , and m the treatment of concentrates from the 
New Rambler Mine, Wyoming Of this about 500 oz were produced 




p IG 35 i ron Meteorite (Sidente) from Canyon Diablo, Arizona Weight 265 
Ibs (Field Columbian Museum ) 

from domestic ores The importations into the United States for the 
same year were about 125,000 oz , valued at $4,500,000 

Platinum-iron, or iron-platinum (Pt Fe), contains from 10 per cent 
to 19 per cent Fe It is usually dark gray or black and is magnetic It 
is found with platinum m sands of the rivers in the Urals Its crystals 
are isometric 

Iron (Fe) occurs in small grains and large masses in the basalt at 
Ovifak, Disko Island, W Greenland, and at a few other points in Green- 
land, and alloys consisting mainly of iron are found in the sands of some 
rivers in New Zealand, Oregon and elsewhere The native metal always 
contains some nickel The most common occurrence of iron, however, is 
m meteorites (Fig 25) In these bodies also it is aUoyed with Ni When 



66 



DESCRIPTIVE MINERALOGY 



polished and treated with nitric acid, surfaces of meteoric iron exhibit 
penes of lines (Widmanstatten figures), that are the edges of plates of 
different composition (Fig 26) These are so arranged as to indicate 
that the substance crystallizes in the isometric system 

Iridium (Ir Pt) and platin-iridium (Pt Ir) are alloys of indium and 
platinum found as silver- white grains with a yellowish tinge, associated 
with platinum in the sands of rivers in the Urals, Burmah and Brazil 
Their hardness is 6 to 7, and density 22 7 The mineral is isometric 
and its fusing point is between 2i5o-225o. 




FIG 26 Widmanstatten Figures on Etched Surface of Meteorite from Toluca, 
Mexico (One-half natural size ) (Field Columbian Mit\cntn ) 

Palladium (Pd) is usually alloyed with a little Pb and Ir It is 
found in small octahedrons and cubes and also in radially fibrous grams 
in the platinum sands of Brazil, the Urals and a few other places It is 
whitish steel-gray in color, has a hardness of 4 to 5 and a density of 
ii 3 to ii 8 It fuses at about 1549 Its crystallization is isometric 
About 2,390 oz of the metal were produced in the United States during 
1912, but all of it was obtained during the refining of bullion. The 
imports were 4,967 oz , valued at $213,397 

Allopalladium (Pd) is probably a dimorph of palladium It is found 
in six-sided plates that are probably rhombohedral, intimately asso- 
ciated with gold, at Tilkerode, Harz 



INTRODUCTION THE ELEMENTS 67 

Osmiridium (Os Ir) and mdosmine (Ir Os) are foundm crystals and 
flattened grams and plates that are apparently rhombohedral They 
consist of Ir and Os m different proportions, often with the addition 
of rhodium and ruthenium Osmiridium is tin-white and iridosrmne 
steel-gray Their hardness is 6 to 7 and density 19 to 21 When heated 
with KNOs and KOH, both yield the distinctive chlorine-like odor of 
osmium o\ide (Os04) and a green mass, \\hich, when boiled with 
water, leaves a residue of blue indium oxide Both are insoluble in 
concentrated aqua regia They occur \\ith platinum in the sands of 
rivers m Colombia, Brazil, California, the Urals, Borneo, New South 
Wales, and a few other places They are distinguished from platinum 
by greater hardness, light color and insolubility in strong aqua regia 

The world's product of refined indium is about 5,000 oz , of which 
the United States furnishes about 500 oz Its value is $63 per oz 
Imports into the United States during 1911 were 3,905 oz, valued at 
$210,616 The sources of the metal are native indium, osrniridmm, 
platinum, copper ore and bullion The metal is obtained from the last 
two sources in the refining process 



CHAPTER IV 

THE SULPHIDES, TELLURIDES, SELENIDES, ARSENIDES AND 
ANTIMONIDES 

THE sulphides are combinations of the metals, or of elements acting 
like bases, with sulphur They may all be regarded as derivatives of 
hydrogen sulphide (H 2 S) by the replacement of the hydrogen by some 
metallic element The tellundes are the corresponding compounds of 
EfeTe, and the selemdes of EkSe 

With the same group are also placed the arsenides and the anti- 
monides, derivatives of HsAs and HsSb, because arsenic and antimony 
so often replace m part the sulphur of the sulphides, forming with these 
isomorphous mixtures 

The minerals described in this volume may be separated into the 
following groups and subgroups 

I The sulphides, tellundes and selemdes of the metalloids arsenic, 
antimony, bismuth and molybdenum 

II The sulphides, tellundes, selemdes, arsenides and antimonides 
of the metals 

(a) The monosulphides, etc (Derivatives of HsS, HgSe, HsTe, 

H 3 As, H 3 Sb ) 
(&) The disulphides, etc (Derivatives of 2HsS, 2H2Te, 2HsAs, 

2 H 3 Sb) 

All sulphur compounds when mixed with dry sodium carbonate 
(Na2COs) and heated to fusion on charcoal yield a mass containing 
sodium sulphide (Na2$) If the mass is removed from the charcoal, 
placed on a bright piece of silver and moistened with a drop or two of 
water or hydrochloric acid, the solution formed will stain the silver a 
dark brown or black color (AgsS), which will not rub off The sulphides 
yield the sulphur reaction when heated with the carbonate on platinum 
foil, the sulphates only when charcoal or some other reducing agent is 
added to the mixture before fusing Moreover, the sulphides yield 
sulphureted hydrogen when heated with hydrochloric acid, while the 
sulphates do not. These tests are extremely delicate. By the aid of 



SULPHIDES, TELLURIDES, ETC 69 

the first one the sulphur in any compound may be detected By the 
aid of the others the sulphates may be distinguished from the 
sulphides 

The selemdes are recognized by the strong odor evolved \\hen heated 
before the blowpipe Selenates and selemtes give their odor only after 
reduction with Na2COs 

The tellundes, \\hen wanned with concentrated HoSO-t, dissolve and 
yield a carmine solution from which water precipitates a black gray 
powder of tellurium 

All substances containing arsenic and antimony yield dense white 
fumes when heated on charcoal in the oxidizing flame The fumes of 
arsenic possess a characteristic odor while those of antimony are odorless 
When heated in the open tube, arsenides and compounds \\ith sulphur 
and arsenic yield a very volatile sublimate composed of tiny white crys- 
tals (AS203) The corresponding sublimate for antimomdes and for 
compounds with antimony and sulphur is nonvolatile, or difficultly 
volatile, and apparently amorphous It is usually found on the under 
side of the tube 

THE SULPHIDES, SELENIDES AND TELLURIDES OF 
THE METALLOIDS 

The sulphides of the metalloids include compounds of sulphur with 
arsenic, antimony, bismuth and molybdenum and a selemde and several 
tellundes of bismuth Only the sulphides are of importance. One, 
shbmte (Sb2Ss), is utilized as a source of antimony 

Realgar (As 2 S 2 ) 

Realgar occurs as a bright red incrustation on other substances, 
as compact and granular masses and as crystals implanted on other 
minerals It is usually associated with the bright yellow orpunent 

(P 7i) 

Absolutely pure realgar should have the following composition 

As, 70 i per cent, S, 29 9 per cent The mineral, however, usually 
contains a small amount of impurities It may be looked upon as a 
derivative of H 2 S in which the hydrogen of two molecules is replaced 
by two arsenic atoms, thus* 

H 2 S As=S 

yielding | 
H 2 S As=S, 



70 



DESCRIPTIVE MINERALOGY 




oo P 5b , oio (b) , oP, ooi 
(c), Poo, on (q) and P, 
in M 



Crystals of realgar are usually short and prismatic m habit They 
are monoclmic (prismatic class) with an axial ratio a b c =i 44 
i . 973 and /3=66 5' The characteristic prismatic faces are 
(w)ooP(uo) and (J)ooP2(2io) These with (b) oo P 5b (oio) con- 
stitute the prismatic zone The terminations are (r) \? 00(012) or 
(q) Pob (on) in combination with the basal plane (0 oP(ooi), the 
orthodome (a) (Toi), and one or more of several pyramids (See Fig 
27 ) The crystals are usually small and are 
striated vertically Prismatic angle 1 10 A ilo 

= 105 34' 

The mineral possesses a distinct cleavage 
parallel to (fc)ooPoo and (/) oo P5 It is 
sectile, soft (H= i 5-2), resinous in luster and 
aurora-red or orange in color Its streak is a 
lighter shade, but with the mineral are fre- 
quently intermingled small quantities of orpi- 
FIG 27 Realgar Crystal ment which impart to its streak a distinct 
yellow tinge Its density is 3 56 In thin 
splinters it is often translucent or trans- 
parent, and strongly pleochroic m red and 
yellow tints, but in masses it is opaque Its 
indices of refraction are not known with accuracy, but its double re- 
fraction is strong ( 030) It is a nonconductor of electricity 

When heated on charcoal before the blowpipe realgar catches fire 
and burns with a light blue flame, at the same time giving off dense 
clouds of arsenic fumes and the odor of burning sulphur (SOs) When 
heated in a closed tube it melts, volatilizes and yields a transparent 
red sublimate in the cold parts of the tube 

Its bright red color and its reaction for sulphur distinguish realgar 
from all other minerals but cinnalar, the sulphide of mercury (p 9#) 
It may easily be distinguished from cinnabar by its softness, its low 
specific gravity and the arsenic fumes which it yields when heated on 
charcoal 

On exposure to the air and to light realgar oxidizes, yielding orpi- 
ment (As2Ss) and arsenolite (As20s) 

Syntheses Realgar is often produced in the flues of furnaces m 
which ores containing sulphur and arsenic are roasted Crystals have 
also been produced by heating to 150 a mixture of AsS with an excess 
of sulphur in a solution of bicarbonate of soda sealed m a glass tube 

Occurrence Localities and Origin Realgar occurs in masses asso 
dated with orpiment and m grams scattered through it at all places 



SULPHIDES, TELLURIDES, ETC 71 

where the latter mineral is found It also occurs associated with silver 
and lead ores in many places It is found in crystals implanted on 
quartz and on the walls of cavities in lavas It "is also occasionally 
a deposit from hot springs In the United States it forms seams in a 
sandy clay in Iron Co , Utah Its crystals are found in calcite in San 
Bernardino and Trinity Counties, California, and with orpiment it is 
deposited as a powder by the hot water of the Norns Geyser basin in the 
Yellowstone National Park 

In most cases it is a product of the interaction of arsenic and sul- 
phur vapors. 

Uses The native realgar occurs in too small a quantity to be of 
commercial importance An artificial realgar is employed in tanning 
and m the manufacture of " white-fire " 

Orpiment (As 2 S 3 ) 

Orpiment, though more abundant than realgar, is not a common 
mineral It is usually found m foliated or columnar masses with a. 
bright yellow color Its name a contraction from the Latin aun- 
pigmentum, meaning golden paint refers to this color 

The pure mineral contains 39 per cent of sulphur and 61 per cent 
of arsenic, corresponding to the formula As2Sa It thus contains 
about 9 per cent more sulphur than does realgar. 

The monoclmic orpiment crystals have the symmetry of the pris- 
matic class Their axial ratio is 596 . i * 665 with =89 19' Though 
always small they are distinctly prismatic with an orthorhombic habit 
Their predominant faces are the ortho and clino pmacoids, several 
prisms and the orthodome 

The cleavage of orpiment is so perfect parallel to o P ob (oio) that 
even from large masses of the mineral distinct foliae may be split 
These are flexible but not elastic The mineral, like many other 
flexible minerals, is sectile Its luster is pearly on cleavage faces, 
which are always vertically striated, and is resinous on other surfaces 
The color of pure orpiment is lemon-yellow, it shades into orange 
when the mineral is impure through the admixture of realgar Its 
streak is always of some lighter shade than that of the mineral Its 
hardness is i 5-2 and its density about 34 In small pieces orpiment 
is translucent and possesses an orange and greenish yellow pleochroism 
When heated to 100 it becomes red and assumes the pleochroism of 
realgar. It, however, resumes its characteristic color and pleochroism 
upon cooling. When heated to 150 the change is permanent. The 
mineral is a nonconductor of electricity. 



72 DESCRIPTIVE MINERALOGY 

The chemical properties of orpiment are the same as those described 
for realgar, except that the sublimate in the closed tube is yellow instead 
of red 

Synthesis Orpiment is produced in large plcochroic crystals by 
treatment of arsenic acid with H 2 S under high prcssuie 

Occurrence, Localities and Origin Orpiment occurs in the same 
forms and in the same places as does realgar Small specks of it occur 
on arsenical iron at Edenville, NY It is also found in the deposits 
of Steamboat Springs Nevada The origin of orpiment is similar 
to that of realgar It is also formed by the oxidation of this mineral 

Uses Native orpiment mixed with water and slaked lime is used 
in the East as a wash for removing hair It is also employed as a pig- 
ment in dyeing Most of the As23 of commerce is a manufactured 
product 

STIBNITE GROUP (R>Q 3 ) 

The stibmte group of sulphides contains several isomorphous 
compounds, of which we shall consider only two, viz , Uibmtc 
and Usmuthimte (61283) The general formula of the group is 
m which R stands for Sb or Bi and Q for S 01 Se The gioup is 
orthorhombic (bipyramidal class) All the members have a distinct 
cleavage parallel to the brachypmacoid which yields flexible laminae 

Sfobnite (Sb 2 Sa) 

Stibmte is the commonest and the most important ore of anti- 
mony It is found in acicular and prismatic crys- 
tals, in radiating groups of crystals and m 
fibrous masses 

Chemically, stibmte is the antimony tnsul- 
phide, SboSa, composed of SI), 71 4 per cent 
and S, 28 6 per cent Ab found, however, it 
usually contains small quantities of iron and often 
traces of silver and gold 

, ^ Crystals of stibmte are often very comnh- 

FIG 28 Stibmte Crys- , , ,, 11, i . 

tal M p no (w) ca ^ ec ^ They are orthorhombic with an axial ratio 

OOP So, oio (ft), 2P2^ 99 2 6 * i 10179 and a columnar or acicular 
121 00 and P, iii(.p) habit The most important forms m the pris- 
matic zone are oo P(no) and oo P 56 (oio). The 
prisms are often acutely terminated by P(iu), ^4(431) and 6P2(36i), 
or bluntly terminated by iP(ii3), (Fig 28) Sometimes the crystals 
are rendered very complicated by the great number of their terminal 




SULPHIDES, TELLURIDES, ETC. 73 

planes Dana figures a crystal from Japan that possesses a termina- 
tion of 84 planes no A ilo=89 34' 

Many of the crystals of this mineral, more particularly those with 
an acicular habit, are curved, bent or twisted Nearly "all, whether 
curved or straight, are longitudinally striated 

The cleavage of stibmte is very perfect parallel to oo P 06 (oio), 
leaving striated surfaces The mineral is soft (H=2) and slightly 
sectile Its density is about 4 5 Its color is lead-gray and its streak 
a little darker In very thin splinters it is translucent in red or yellow 
tints In these the indices of refraction for yellow light have been 
determined to be, 0^=4303 and 7=3 194 Surfaces that are exposed 
to the air are often coated with a black or an iridescent tarnish The 
luster of the mineral is metallic It is a nonconductor of electricity 

Stibmte fuses very easily, thin splinters being melted even in the 
flame of a candle When heated on charcoal the mineral yields anti- 
mony and sulphurous fumes, the former of which coat the charcoal white 
in the vicinity of the assay When heated in the open tube SCb is 
evolved and a white sublimate of Sb20s is deposited on the cool walls of 
the tube In the closed tube the mineral gives a faint ring of sulphur 
and a red coating of antimony oxysulphide It is soluble in nitric acid 
with the precipitation of Sb20s 

Stibmte may easily be distinguished from all minerals but the other 
sulphides by the test for sulphur From the other sulphides it is dis- 
tinguished by its cleavage and the fumes it yields when heated on char- 
coal Its closest resemblance is with galena (PbS), which, however, 
differs from it in being less fusible and in yielding a lead globule when 
fused with sodium carbonate on charcoal. Moreover, galena possesses 
a cubic cleavage 

Syntheses Stibnite is produced by heating to 200, a mixture of 
sulphur and antimony with water under pressure, and by the reaction of 
H2S on antimony oxide heated to redness 

Occurrence, Localities and Origin The mineral is found as crystals 
in quartz veins cutting crystalline rocks, and in metalliferous veins asso- 
ciated with lead and zinc ores, with cinnabar (HgS) and barite (BaSO-i) 
The finest crystals, some of them 20 inches in length, come from mines 
in the Province of lyo, on the Island of Shikoku/Japan The mineral 
occurs also m York Co , New Brunswick, in Rawdon township, Nova 
Scotia, at many points in the eastern United States, in Sevier Co , 
Arkansas, in Garfield Co , Utah, and at many of the mining districts in 
the Rocky Mountain States 

In Arkansas stibmte is in quartz veins following the bedding planes 



74 DESCRIPTIVE MINERALOGY 

of shales and sandstones With it are found many lead, zmc and 
iron compounds and small quantities of rarer substances In Utah 
the mineral occurs m veins unmixed AMth other minerals, except its 
o\\n oxidation products The veins follow the bedding of sandstones 
and conglomerates Here, as in Arkansas, the stibnite is believed to 
have been deposited by magmatic waters 

Uses Stibnite was powdered by the ancients and used to color the 
eyebrows, eyelashes and hair At present it is used to a slight extent in 
vulcanizing rubber and in the manufacture of safety matches, percussion 
caps, certain kinds of fireworks, etc Its principal value is as an ore of 
antimony Practically all of the metal used in the arts is obtained 
from this source Antimony is chiefly valuable as an alloy with other 
metals With tin and lead it forms type metal The principal alloys 
with tin are britannia metal and pewter With lead, tin and copper 
it constitutes babbit metal, a hard alloy used in the construction of 
locomotive and car journals, and with other substances it enters into 
the composition of other alloys used for a variety of purposes The 
double tartrate of antimony and potassium is the well known tartar 
emetic. The pigment, Naples yellow, is an antimony chromate. 

Production The total quantity of stibnite mined in the world can- 
not be accurately estimated That mined in the United States is very 
small in amount, most of the antimony produced m this country being 
obtained in the form of an antimony alloy as a by-product in the smelting 
of antunomal lead ores 

Bismuthinite (Bi 2 S 3 ) 

Bismuthimte is completely isomorphous with stibnite It rarely, 
however, occurs in acicular crystals, but is more frequently in foliated, 
fibrous or dense masses 

Its axial ratio is 968 i : 985. 

The angle noAiTo = 88 8' 

The mineral resembles stibnite in color and streak, but its surface is 
often covered with a yellowish iridescent tarnish Its fusibility and 
hardness are the same as those of stibnite but its density is 6 8-7 i It 
is an electrical conductor 

In the open tube the mineral yields S02 and a white sublimate 
which melts into drops that are brown while hot, but change to opaque 
yellow when cold On charcoal it yields a coating of yellow 81203 which 
changes to a bright red Bils when moistened with potassium iodide 
The mineral dissolves in hot nitric acid, forming a solution, which upon 
the addition of water gives a white precipitate of a basic bismuth nitrate. 



SULPHIDES, TELLURIDES, ETC ?5 

Bismuthmite is distinguished from stibmte by the coating on char- 
coal and by its complete solubility in HNOa 

Syntheses Crystals have been obtained by cooling a solution of 
m molten bismuth, and by cooling a solu.ion made by heating 
BioSs m a solution of potassium sulphide in a closed tube at 200. 

Occurrence , Localities and Origin Bismuthmite occurs as a constit- 
uent of veins associated \vith quartz, bismuth and chalcopynte, in which 
it was probably formed as a product of pneumatolytic processes It is 
found at Schneeberg and other points in Saxony, at Redruth and 
elsewhere in Cornwall, near Beaver City, Utah, in a gold-bearing veiii 
at Gold Hill, Rowan County, N C , and in a vein containing benl, 
garnet, etc , in granite at Haddam, Conn 

TETRADYMITE GROUP 

This group comprises a series of tellundes and selemdes of bismuth 
that have not been satisfactorily differentiated because of the lack of 
accurate analyses 

Tetradymite, the best known member of the group, is probably an 
isomorphous mixture cf bismuth tellunde and bismuth sulphide of the 
formula Bi2(Te 8)3 It occurs in small rhombohedral cnstals with the 
axial ratio i . i 587 and loli A 1101 = 98 58' Its crystals are bounded 
by rhombohedrons (R(ioTi) and 2R(202ii)) and the basal plane 
(oP(oooi)). Interpenetration fourlings are common with |R(oil2), 
the twinning plane The mineral is, however, more frequently found 
in foliated and granular masses. Its color is lead-gray It possesses a 
perfect cleavage parallel to the base Its hardness is i 5-2 and its 
density about 74 It is a good electncal conductor Its best known 
occurrences are Zsubkau, Hungary, Whitehall, Va, in Davidson 
County, N C , near Dahlonega, Ga , near Highland, Mont , and at 
the Montgomery Mine and at Bradshaw City in Arizona It occurs in 
quartz veins associated with gold in the gold sands of some streams 

The other members of the group appear to be completely isomorphous 
with tetradymite. They vary m color from tin-white through gray to 
black. 

Molybdenite (MoS) 

This mineral, which is the sulphide of the rare metal molybdenum, 
does not occur in large quantity, but it is so widely distributed that it 
seems to be quite abundant It occurs principally in black scales scat- 



76 DESCRIPTIVE MINERALOGY 

tered through coarse-grained, crystalline, siliceous rocks and granular 
limestones and in black or lead-gray foliated masses 

The theoretical composition of molybdenite is 40 per cent sulphur 
and 60 per cent molybdenum Usually, however, the mineral contains 
small quantities of iron and occasionally other components 

Crystals of molybdenite are exceedingly rare Scales and plates 
with hexagonal outlines are often met with but they do not usually pos- 
sess sufficiently perfect faces to >ield accurate measurements The 
measurements that have been obtained appear to indicate a holohedral 
hexagonal symmetry with an axial ratio i i 908 

The cleavage of molybdenite is very perfect parallel to the base. 
The laminae are flexible but not elastic The mineral is sectile and so 
soft that it leaves a black mark when drawn across paper Its density 
is 4 7. Its luster is metallic, color lead-black, and streak greenish 
black In very thm flakes the mineral is translucent with a green tinge 
Otherwise it is opaque It is a poor conductor of electricity at ordi- 
nary temperature, but its conductivity increases with the temperature 

In the blowpipe flame molybdenite is infusible It, however, im- 
parts to the edges of the flame a yellowish green color Naturally, it 
yields all the reactions for sulphur, and in the open tube it deposits a 
pale yellow crystalline sublimate of MoOs Molybdenite is decomposed 
by nitric acid with the production of a gray powder (MoOs) 

By its color, luster and softness molybdenite is easily distinguished 
from all minerals but graphite From this it is distinguished by its 
reaction for sulphur Moreover, a characteristic test foi all molyb- 
denum compounds is the dark blue coating produced on porcelain when 
the pulverized substance is moistened with concentrated sulphuric 
acid and then heated until almost dry Before this test can be applied 
to molybdenite, the mineral must first be powdered and then oxi- 
dized by roasting in the air for a few minutes or by boiling to dryness 
with a few drops of HNOs 

Syntheses Crystalline molybdenite has been prepared by the action 
of sulphur vapor or EfeS upon glowing molybdic acid It has also been 
produced by heating a mixture of molybdates and lime, in a large excess 
of a gaseous mixture of HC1 and EfeS. 

Occurrence, Localities arid Origin Molybdenite generally occurs 
^embedded as grams in limestone and in the crystalline silicate rocks, 
as, for instance, granite and gneiss, and as masses in quartz veins, at 
Arendal, Norway, at Blue Hill Bay, Maine, at Haddam, Conn , m 
Renfrew Co , Ontario, and at many points in the far western states 
It is thought to be of pneumatolytic origin. 



SULPHIDES, TELLURIDES, ETC 77 

Uses The mineral is the principal ore of the metal molybdenum, 
the salts of which are important chemicals employed principally in 
analytical work, especially in the detection and estimation of phosphoric 
acid The mol^bdate of ammonia (NH^MoO^ the principal salt 
employed in analytical processes, is easily obtained by roasting a mix- 
ture of sand and molybdenite and treating the oxidized product with 
ammonia Other molybdenum salts are used for giving a green color 
to porcelain The metal is used in an alloy (ferro-mol}bdenum) for 
hardening steel, as supports for the lower ends of tungsten filaments in 
electric lamps and for making ribbons used in electric furnaces 

Production There was no production of molybdenite in North 
America during 1912 The imports of the metal into the United States 
aggregated 3 5 tons, valued at $4,670. The value of the imports 
of the ore is not known* 

THE SULPHIDES, SELEWIDES, ETC., OF THE METALS 
THE METALLIC MONOSULPHIDES, ETC 

The metallic monosulphides, monoselemdes, etc , are compounds 
in which the hydrogen of H 2 S, H 2 Se, H 2 Te, HsAs, and HsSb are 
replaced by metals Among them are some of the most important 
ores 

They may be separated into several groups of which some are 
among the best defined of all the mineral groups, while others consist 
simply of a number of minerals placed together solely for convenience 
of description In addition, there are a few members of this chemical 
group which seem to have no close relationship with any other mem- 
bers These are discussed separately 

The groups described are as follows: 

The Dyskrasite Group 
The Galena Group 
The Chalcocite Group. 
The Blende Group 
The Millerite Group 
The Cinnabar Group. 

DYSKRASITE GROtJP 

This group includes a number of arsenides and antimonides, some 
of which apparently contain an excess of the metal above that neces- 
sary to satisfy the formulas HsAs and HsSb. Although their com- 



78 DESCRIPTIVE MINERALOGY 

position is not understood, they are generally regarded as basic com- 
pounds A few of them are well crystallized, but their composition is 
doubtful, because of the difficulty of obtaining pure material for anal- 
yses Some of them are probably mixtures The members of the 
group, all of which are ccmparatrvely rare, are wkitneyite (CuoAs), 
algodomte (CueAs), domeykite (CuaAs), horsfordite (Cu^Sb) and dyskras- 
ite (AgaSb) Other minerals are known which may properly be placed 
here, but their identity is doubtful The only two members that need 
further discussion are domeykite and dyskrasite 

Domeykite (CuaAs) is known only in disseminated particles and 
in botryoidal and dense masses and small orthorhombic crystals It 
may be a mixture of several components, which in other proportions 
form algodomte It is tin-white or steel-gray and opaque It becomes 
dull and covered with a yellow or brown iridescent tarnish when ex- 
posed to the air Its hardness is 3-4 and density about 73 It is the 
most easily fusible of the copper arsenides Its principal occurrences 
are m the silver mines of Copiapo and Coquimbo in Chile, associated 
T\ith native copper at Cerro de Paracabas, Guerrero, Mexico, at Shel- 
don, Portage Lake, Michigan, and on Michipicoten Island, in Lake 
Superior, Ontario The last two occurrences are in quartz veins 

Dyskrasite (AgaSb) occurs in foliated, granular and structureless 
masses and rarely in small orthorhombic crystals with an hexagonal 
habit Their axial ratio is 5775 i . 6718, Twinning is frequent, 
yielding star-shaped aggregates The mineral has a silver-white color 
and streak, but its exposed surfaces are often tarnished yellow or bUck 
It is opaque and sectile Its hardness is 3 5-4 and density about 9 6 
It is a good electrical conductor Dyskrasite is soluble in HNO^ 
leaving a white sediment of Sb20s It occurs principally in the silver 
mines of central Europe, and especially near Wolfach, Baden, St 
Andreasberg, Harz, and at Carnzo, in Copiapo, Chile. 

GALENA GROUP 

The minerals comprising the galena group number about a dozen 
crystallizing m the holohedral division of the regular system (hex- 
octahedral class) They possess the general formula RQ in which 
R represents silver, lead, copper and gold, and Q sulphur, selenium 
and tellurium The group may be divided into silver compounds and 
lead compounds, thus (A) argentite (Ag 2 S), hessite (Ag 2 Te), petzite 
((Ag Au) 2 Te), naumanmte (Ag 2 Se), agmlante (Ag 2 (Se S)), jalpaitc 



SULPHIDES, TELLURIDES, ETC 79 

((Ag Cu) 2 S) and eukante ((Ag Cu) 2 Se), and (B) galena (PbS\ altaite 
(PbTe), and dausttalite (PbSe) Of these onh two are of importance, 
viz, galena, and argentite Hessite and petzite are comparative!} 
unimportant ores of gold 

Argentite (AgoS) 

Argentite, though not very widespread m its occurrence, is an 
important ore of silver It is found in masses, as coatings, and in crys- 
tals or arborescent groups of crystals 

Argentite contains 87 i per cent silver and 12 9 per cent sulphur when 
pure It is usually, however, impure through the admixture of small 
quantities of Fe, Pb, Cu, etc 

The forms most frequently observed on argentite crystals are 
ooOoo(ioo), ooO(no) and 0(in), though various wOoo (hid) and 
wOm (hll) forms are also met Tvith The crystals are often distorted 
and often they are grouped in paiallel growths of different shapes 
Twinning is common, with 0(in) the twinning plane The twins 
are usually penetration twins The habit of most crystals is cubical 
or octahedral 

Argentite is lead-gray in color Its streak is a little darker The 
mineral is opaque Its luster is metallic, its hardness about 2 25 and* 
density 73 It is sectile, has an imperfect cleavage and is a conductor 
of electricity 

When heated on charcoal argentite shells and fuses, yielding sulphur 
fumes and a globule of silver It is soluble m nitric acid 

Argentite is easily recognized by its color, its sectility, the fact that 
it yields a silver globule when fused with Na2COs on charcoal and yields 
the sulphur test with a silver corn 

Syntheses Crystals of argentite may be obtained by treating red 
hot silver with sulphur vapor or dry HfcS, and by heating silver and SCb 
in a closed tube at 200 

Occurrence, Localities and Origin The mineral is found in the second- 
ary enrichment zones of veins associated with silver and other sulphides 
in many silver-mining districts In Nevada it is an important ore at 
the Comstock lode and in the Cortez district It is found also near 
Port Arthur on the north shore of Lake Superior, in Ontario, and asso- 
ciated with native silver in the copper mines of Michigan The ores of 
Mexico, Chile, Bolivia and Peru are composed largely of this mineral. 

Production Much of the silver produced in this country is obtained 
from argentite, though by no means so great a quantity as is obtained 
from other sources* 



80 DESCRIPTIVE MINERALOGY 



Hessite (Ag 2 Te) and Petzite ((Ag Au) 2 Te) 

These two minerals, though comparatively rare, are prominent 
sources of gold and silver in some mining camps They usually occur 
together associated with other sulphides. 

Hessite is the nearly pure silver tellunde and petzittf, &n isomorphous 
mixture of gold and silver tellundes, as indicated by the following analy- 
ses of materials from the Red Cloud Mine, Boulder Co , Colorado 





Te 


Ag 


Au Cu 


Pb Fe 


Zn 


Si0 2 


Total 


I 


3786 


59 9i 


22 17 


45 i 35 






99 96 


II 


34 9i 


50 66 


13 09 7 


17 36 


IS 


70 


100 01 


III 


32 97 


40 80 


24 69 


i 28 


21 


05 


100 00 



The minerals crystallize in all respects like argentite They are 
opaque and lead-gray to iron-black in color, sectile to brittle, have a 
hardness between 2 and 3 and a specific gravity of 8 3-9, increasing with 
the percentage of gold present They are good conductors of electricity 

Before the blowpipe, both minerals melt easily to a black globule, at 
the same time coloring the reducing flame greenish and giving the odor 
of tellurium fumes When acted upon by the reducing flame, the globule 
becomes covered with little crystals of silver With Na2COs on charcoal 
both minerals yield a globule of silver, but the globule obtained from 
hessite dissolves in warm HNOs, while that obtained from petzite 
becomes yellow (gold) In the open tube both yield a white sublimate 
of TeO2 which melts, when heated, to colorless drops When heated 
with concentrated H^SCU, they give a purple or red solution which, upon 
the addition of water, loses its color and precipitates blackish gray, 
powdery tellurium. The minerals dissolve in HNOs From this solu- 
tion HC1 throws down white silver chloride 

Both the minerals resemble very closely many forms of argentite 
and galena, from which, however, they may be distinguished by the 
reactions for tellurium Petzite and hessite may be distinguished from 
one another by the test for gold Moreover a fresh surface of hessite 
blackens when treated with a solution of KCN, whereas a surface of 
petzite remains unaffected 

Syntheses Octahedrons of hessite are obtained by the action of 
tellurium vapor upon glowing silver in an atmosphere of nitrogen, and 
dodecahedrons of petzite upon similar treatment of gold-silver alloy 

Origin Both minerals are believed to be primary deposits orig- 
inating in magmatic solutions They occur in veins with native gold, 
quartz, fluonte, dolomite, and various sulphides and other tellundes. 



SULPHIDES, TELLURIDES, ETC 81 

Localities These tellundes, together uith others to be described 
later (p 113), are important sources of silver and gold in the mines at 
Nagyag, Transylvania, at Cripple Creek and in Boulder Co , Colo , and 
at Kalgoorhe, W Australia The quantity of tellundes mined is con- 
siderable, but since it is impracticable to separate these t\\o tellundes 
from the other compounds of gold and silver mined with them, it is im- 
possible to estimate the proportion of the metals obtained from them 

Galena (PbS) 

Galena, the most important ore of lead, occurs in great lead-gray 
crystalline masses, in large and small crystals, in coarse and fine granukr 
aggregates, and in other less common forms Much galena contains 
silver, m which case it becomes an important ore of this metal 

Galena rarely approaches the theoretical composition 13 4 per cent 
cf sulphur and 86 6 per cent of lead It usually contains small quanti- 
ties of the sulphides cf silver, zinc, cadmium, copper and bismuth and 
in some cases native silver and gold When the percentage of silver 
present reaches 3 oz per ton the mineral is ranked as a silver ore This 
silver is apparently present in some cases as an isomorphous mixture 
of silver sulphide and m other cases in distinct 
minerals included within the galena 

Galena crystals usually possess a cubical habit, 
though crystals with the octahedral habit are 
very common The principal forms observed are 

ooOoo(ioo), 0(in), ooO(no), mQoo(klo) and 

mQm (hlT) (Figs 29 and 30) Twins are common, 
\\ith the twinning face FlG 2 9 -Galena ays- 

Galena is well characterized by its lead-gray * * ' J ,? 
color, its perfect cleavage parallel to the cubic faces an ^ Q, ni (o) 
and by its great density (8 5) Its luster is me- 
tallic and its hardness about 2 6 Its streak is grayish black. It is a 
good conductor of electricity 

On charcoal galena fuses, yielding sulphurous fumes and a globule 
of metallic lead, which may easily be distinguished from a silver globule 
by its softness The charcoal around the assay is coated with a yellow 
sublimate of lead oxide (PbO) The mineral is soluble in HNOs with 
the separation of sulphur 

Its color and luster distinguish galena from nearly all minerals but 
s Unite From this mineral it is easily distinguished by its more difficult 
fusibility, by its cleavage, and by the fact that it does not yield the anti- 
mony fumes when heated on charcoal 




82 



DESCRIPTIVE MINERALOGY 



Galena weathers readily to the sulphate (anglesite) and carbonate 
(cerussite) , consequently it is usually not found m the upper portions 
of veins that are exposed to the action of the air. 

Syntheses Crystals of galena result from heating a mixture of 
lead oxide with NEUCl and sulphur, and from treatment of a lead salt 
with HgS at a red heat Small crystals have been produced by heating 




FIG 30 Galena Crystals (<*>OQ(IOO) and O(in)) partly covered by Manasitc, 
from the Joplm District, Mo (After U T 6 T Smith and C I 1 bitbentlial ) 

in a sealed glass tube at 8o-9o pulverized cerussite (PbCO,j) in a water 
solution of HkS 

Origin Veins of galena containing silver (silver-lead) were probably 
produced by ascending solutions emanating from bodies of igneous 
rocks, while the galena in limestone was probably deposited by ground- 
water that dissolved the sulphide from the surrounding sedimentary 
rocks Galena is also in some cases a metamorphic product 

Occurrence The mineral occurs very widely spread It is found 
in veins associated with quartz (SiCfe), calcite (CaCOa), bante (BaSOi) 
or fluonte (CaF2) and various sulphides, especially the zinc sulphide, 
sphalerite, in irregular masses filling clefts and cavities in limestone, 



SULPHIDES, TELLURIDES, ETC 83 

in beds, and in stalactites and other forms characteristic of water 
deposits 

It occurs also as pseudomorphs after pyromorphite the lead phos- 
phate The form that occurs in veins is often silver bearing, while that 
in limestone is usually free from silver 

Localities Galena is mined m Cornwall and in Derbyshire, Eng- 
land, in the Moresnet district, Belgium, at various places in Silesia, 
Bohemia, Spam and Australia In the United States it occurs in veins at 
Lubec, Me , at Rossie, St Lawrence Co , N Y , at PhoenL\ville, Penn , at 
Austin's Mines in Wythe Co , Va , and at many other places It is 
mined for silver in Mexico, at Leadville, Colo , at various points in 
Montana, in the Cceur d'Alene region in Idaho and at many other places 
in the Rocky Mountain region 

The most extensive galena deposits in this country are in Missouri, 
m the corner made by the states of Wisconsin, Illinois and Iowa, and 
in Cherokee Co , Kansas In these districts the galena, associated 
with sphalerite (ZnS), pynte (FeS2), smithsomte (ZnCOs), calamine 
((ZnOH) 2 SiO 3 ), cerussite (PbC0 3 ), calcite (CaCOa) and other minerals, 
fills cavities in limestone 

Extraction of Lead and Silver from Galena The ore is first crushed 
and concentrated by mechanical or electrostatic methods, and the 
concentrates are roasted to convert them into oxides and sulphates 
The mass is then heated without access of air, sulphur dioxide being 
driven off, leaving metallic lead carrying impurities, or a mixture of 
lead and silver 

The processes employed in refining the impure lead vary with the 
nature of the impurities 

Uses Galena is employed to some extent in glazing common 
stoneware It is also used in the preparation of white lead and other 
pigments As has alrercly been stated, it is the most important ore of 
lead and a very important ore of silver 

The metal lead finds many uses in the arts Its most common 
use is for piping Its alloys, type metal, pewter and babbitt metal 
have already been referred to (p 74) Solder is an alloy of tin and lead, 
Wood's metal a mixture of lead, bismuth, tin and cadmium The spe- 
cial characteristic of Wood's alloy is its low fusion point (70) 

Production The total production of galena by the different coun- 
tries of the world cannot be given, but the world's production of lead 
in 1912 was 1,277,002 short tons The total quantity of lead pro- 
duced by the United States from domestic ores in the same year was 
about 415,395 tons, valued at $37,3 8 5>55 M st of this was obtained 



84 DESCRIPTIVE MINERALOGY 

from galena About 171,037 tons were soft lead, smelted from ores 
mined mainly for their lead and zinc contents, and the balance from 
ores mined partly for their silver The importance of galena as an ore 
of silver may be appreciated from the fact that of the $39,197,000 
worth of this metal produced in the United States during 1912, silver 
to the value of about $12,000,000 was obtained from lead ores or from 
mixtures of lead and zinc ores 

Altaite (PbTe) and clausthalite (PbSe) both resemble galena m 
appearance Both occur commonly in fine-grained masses, but they 
are also found in cubic crystals Altaite is tin-white, tarnishing to 
yellow or bronze, and clausthahte is lead-gray Their hardness is 2 5-3 
and specific gravity about 8 i They are associated with silver and lead 
compounds principally in the silver mines of Europe and South America 
Altaite is known also from several mines in California, Colorado and 
North Carolina They are distinguished from one another and from 
galena by the tests for Te and Se 

CHALCOCITE GROUP 

The chalcocite group includes four or five cuprous and argentous 
sulphides, selemdes and tellundes They all crystallize in the ortho- 
rhombic system (rhombic bipyramidal class) often with an hexagonal 
habit, and are isomorphous The best known members of the group 
are chalcoc^te (Cu2S) and stromeyente (Cu AgJgS, but only the first- 
named is common Although these minerals are orthorhombic, never- 
theless Cu2S is known to exist also in isometric crystals, in which form 
it is isomorphous with argentite Moreover, stromeyente is an iso- 
morphous mixture of Ag2$ and Cu2S Therefore, it is inferred that 
and AggS are isomorphous dimorphs 



Chalcocite (Cu 2 S) 

Chalcocite (Cu2S), the cuprous sulphide, is an important ore of 
copper though by no means as widely spread as the iron-copper sul- 
phide, chalcopyrite It is usually found in black masses with a dull 
metallic luster and as a black powder, though frequently also in crys- 
tals It is a common constituent of the enrichment zone of many veins 
of copper ores, 

The best analyses of chalcocite agree closely with the formula 
given above, requiring the presence of 20 2 per cent of sulphur and 
79 8 per cent of copper Iron and silver are often present in the mineral 
in small quantity 



SULPHIDES, TELLURIDES, ETC 85 

In crystallization chalcocite is orthorhombic (rhombic bipyramidal 
class) with the axial ratio 5822 . i 9701 Its crystals contain as 
their predominant forms oP(ooi), ooP(no), ooP 00(010), P(in), 

a series of prisms of the general symbol -P(iiA). and several bra- 

m 

chydomes Many cf the crystals are elongated parallel to #, and 
others are so developed as to possess an hexagonal habit (Fig 31) 
Twins are common according to several laws When the twinning plane is 
|P (112) the twins are usually cruciform (Fig 32) The zone ooi oio 
is often striated through oscillatory combinations iioAiib=6o 25' 
The cleavage of chalcocite is indistinct, its fracture is conchoidal 
Its hardness is 2 5-3 and density about 5 7. Its streak, like its color, 





FIG 31 FIG 32 

FIG 31 Chalcocite Crystal oP, ooi (c), p So , oio (ft), o P, no (m), 2? , 

021 (d), |P w, 023 (<0, P, iii (p) and JP, 113 00 

FIG 32 Complex Chalcocite Twin, with o P, no (m) and |P, 112 (p) the Twinning 

Planes 

is nearly black, but exposed surfaces are often tarnished blue or green, 
probably through the production of thin films of other sulphides like 
covellite (CuS), chalcopynte (FeCuSa), etc The mineral is an excel- 
lent conductor of electricity 

In the open tube or on charcoal chalcocite melts and yields sul- 
phurous fumes 

When mixed with Na2COs and heated a copper globule is produced. 
The mineral dissolves in nitric acid with the production of a solution 
that yields the test for copper. 

Upon exposure to the air chalcocite changes readily to the oxide, 
cupnte (CusO), and the carbonates, malachite and azurite. In the 
presence of siliaous solutions it may give rise to the silicate, chrysocolla 

(P 44i) . 

A pseudomorph of chalcocite after galena is known as Aomnfe. 



86 DESCRIPTIVE MINERALOGY 

It occurs at the Canton Mine m Georgia and in the Polk Co copper 
mines in Tennessee Pseudomorphs after many other copper min- 
erals are common 

Chalcocite is recognized by its color and crystallization Massive 
varieties are distinguished from argentite by greater bnttleness and the 
reaction for copper, from bormte (CusFeSs) by the fact that it is not 
magnetic after roasting 

Syntheses Crystals of chalcocite have been made in many ways, 
more particularly by heating the vapors of CuCb and H^S, and by 
gently warming CuaO in B^S Measurable crystals have been observed 
on old bronze that has been immersed m the waters of hot springs for 
a long time 

Occurrence , Localities and Origin The mineral is a common prod- 
uct of the alteration of other copper compounds in the zone of secondary 
enrichment of sulphide veins. It is therefore present at most localities 
of copper minerals One of the best known occurrences is Butte, 
Mont 

Fine crystals of chalcocite occur in veins and beds at Redruth and 
at other places m Cornwall, England, at Bristol m Connecticut, and 
at Joachunthal in Bohemia The massive variety is known at many 
places In the United States it occurs m red sandstone at Cheshire 
in Connecticut It is found also in large quantities near Butte City in 
Montana, and in Washoe and other counties in Nevada, and indeed 
in the veins of most copper producing mines In Canada it is present 
with chalcopynte and bormte at Acton, Quebec, and at several places 
in Ontario north of Lake Superior 

Extraction of Copper Chalcocite rarely occurs alone in large 
quantity. In ores it is usually mixed with other compounds of copper, 
and is treated with them in extracting the metal (see p. 133). 

Stromeyerite ((Ag Cu)2S) is usually massive, but it occurs also in 
simple and twinned crystals similar to those of chalcocite Their axial 
ratio is 5822 i : 9668, almost identical with that of chalcocite The 
mineral is opaque and metallic Its color and streak are dark steel- 
gray Its hardness is 2 5-3 and density about 62 It is soluble m 
nitric acid It occurs associated with other sulphides in the ores of 
silver and copper mines at Schlangenberg, Altai, Kupferberg, Silesia, 
Coquimbo, Copiap6, and other places in Chile, and in a few mines m 
California, Arizona, and Colorado, 



SULPHIDES, TELLURIDES, ETC 87 

BLENDE GROUP 

The blende group of minerals comprises a series of compounds whose 
general formula like that of the galena group is RQ In the blendes R 
stands for Zn, Cd, Mn, Ni and Fe and Q for S, Se and Te 

The blendes are ail transparent or translucent minerals of a lighter 
color than galena They constitute an isodimorphous group of a dozen 
or more members crystallizing in the tetrahedral division of the regular 
system (hextetrahedral class), and in hemimorphic holohedral forms of 
the hexagonal system (dmexagonal-pyramidal class) The group may 
be divided into two subgroups known respectively as the sphalerite 
and the wurtzite groups 

SPHALERITE DIVISION 

The most important member of this division of the blende group is 
the mineral sphalerite. This, like the other less well known members, 
crystallizes in the hemihedral division of the regular system with various 
tetrahedrons as prominent forms The other members of the group 
are alabandite (MnS), and an isomorphous mixture of FeS and NiS, 
pentlandite 

Sphalerite (ZnS) 

Sphalerite, one of the very important zinc ores and one of the most 
interesting minerals from a crystallographic standpoint, occurs in amor- 
phous and crystalline masses and in handsome crystals and crystal groups 
Botryoidal and other imitative masses are common 

Pure white sphalerite consists of 67 per cent of Zn and 23 per cent of 
sulphur The colored varieties usually contain traces of silver, iron, 
cadmium, manganese and other metals Sometimes the proportion of 
the impurities is so large that the mineral containing them is regarded as 
a distinct variety Two analyses of American sphalerites are as follows 

S Zn Cd Fe Total 

Franklin Furnace, N J 32 22 67 46 tr 99 68 

Jophn, Mo 32 93 66 69 42 100 04 

The hemihedral condition of sphalerite is shown in the predominance 
of tetrahedrons among its crystal forms and by the symmetry of its 

-Q3. _ 

etched figures (Fig. 33). Its most common forms are ~(3 21 ) and 
other hextetrahedrons, (221), ^-(331) and other deltoid-dodeca- 



88 



DESCRIPTIVE MINERALOGY 



hedrons and 303(311) and other tristetrahedrons In addition, 
ooO<(ioo) and ooO(no) are quite common (Fig 34) Twins are 
abundant Their twinning plane is and their composition face either 
(Fig 35), or a plane perpendicular to this Through twinning, the 
crystals often assume a rhombohedral habit 

The cleavage of sphalerite is perfect pardlel to ooO(no) From a 
compact mass of the mineral a fairly good dodecahedron may some- 
times be split Its fracture is conchoidal When pure the mineral is 
transparent and colorless As usually found, however, it is yellow, 
translucent and black, brown, or some shade of red Its streak is 
brownish, yellow or white. The yellow masses look very much like 




FIG 33 



FIG 34 



FIG 35 



FIG 33 Tetrahedral Crystal of Sphalerite Bounded by oo o (101) and O (in 
and ill), Illustrating the Fact that Its Octahedral Faces Fall into Two Groups 

FIG 34 Sphalerite Crystal oo 0, no (<*), and-f -, 311 (m) 
FIG 35 Sphalente Octahedron Twinned about 0(ni) 

lumps of rosin. The hardness of sphalerite is between 3 5 and 4, and its 
density about 4 Its luster is resinous The minei al is difficultly fusible, 
and is a nonconductor of electricity Its index of refraction (ri) for 
yellow light is 2 369. 

Sphalerite when powdered always yields tests for sulphur under 
proper treatment On charcoal it volatilizes slowly, coating the coal 
with a yellow sublimate when hot, turning white on cooling When 
moistened with a dilute solution of cobalt nitrate and heated m the 
reducing flame, the white coating of ZnO turns green The mineral dis- 
solves in hydrochloric acid, yielding sulphuretted hydrogen 

By oxidation sphalerite changes into the sulphate of zinc, and by 
other processes into the silicate of zinc, calamine, or the carbonates, 
smithsonite and hydrozincite. 



SULPHIDES, TELLURIDES, ETC 89 



Syntheses Sphalerite crystals have been made by the action of 
upon zinc chloride \ apor at a high temperature They are also often 
produced in the flues of furnaces in which ores containing zinc and sul- 
phur are roasted 

Occurrence and Origin Sphalerite occurs disseminated through lime- 
stone, in streaks and irregular masses in the same rock, and in veins cut- 
ting crystalline and sedimentary rocks It is often associated with 
galena The material in the veins is often crystallized Here it is asso- 
ciated with chalcopynte (CuFeS2), fluonte (CaF 2 ), bante (BaSCX), 
sidente (FeCOs), and silver ores When in veins it is in some cases the 
result of ascending hot waters and in other cases the product of down- 
ward percolating meteoric water. Much of the disseminated ore is a 
metamorphic contact deposit. 

Localities Crystallized sphalerite is found abundantly at Alston 
Moor, Cumberland, England, at vanous places in Saxony, in the Bin- 
nenthal, Switzerland; at Broken Hill, N S Wales, and in nearly all 
localities for galena. Handsome, transparent, deavable masses are 
brought from Pilos de Europa, Santander, Spain. Stalactites are 
abundant near Galena, 111 

The principal deposits of economic importance in America are those 
in Iowa, Wisconsin, Missouri and Kansas, where the sphalerite is asso- 
ciated with other zinc compounds and with galena forming lodes in 
limestone, and at the silver and gold mines of Colorado, Idaho and Mon- 
tana 

Extraction of the Metal In order to obtain the metal from sphalerite, 
the ore is usually first concentrated by flotation or other mechanical 
processes. The concentrates are then converted into the oxide by roast- 
ing and the impure oxide is mixed with fine coal and placed in clay retorts 
openmg into a condenser. These are gradually heated The oxide is 
reduced to the metal, which being volatile distils over into the con- 
denser, where it is safely caught. Other processes are based on wet 
chemical methods 

Uses of Zinc Zinc is used extensively in galvanizing iron wire and 
sheets It is also employed in the manufacture of important alloys 
such as brass, and in the manufacture of zmc white, which is the oxide 
(ZnO), and other pigments A solution of the chloride is used for pre- 
serving timber. Argentiferous zinc is the source of a considerable quan- 
tity of silver. 

Production The figures showing the quantity of sphalerite pro- 
duced in the zinc-producing countries are not available The total 
amount of metallic zmc produced in the year 1912 was 1,070,045 tons, 



90 DESCRIPTIVE MINERALOGY 

valued at $44,699,166, of which the United States produced from domestic 
ores 323,907 tons, and in addition used, in the making of zinc compounds, 
about 55,000 tons Of this aggregate, Missouri produced about 149,560 
tons Most of the metal was obtained from sphalerite, but a large 
part came from other ores The quantity of silver produced in refining 
zinc ores was 664,421 oz , valued at $408,619 

Alabandite (MnS) is isomorphous with sphalerite It usually 
occurs, however, in dense granular aggregates of an iron-gray color 
Its streak is dark green It is opaque and brittle Its hardness is 3-4 
and density 39 It is not an electrical conductor When heated on 
charcoal in the reducing flame it changes to the brown oude of man- 
ganese and finally melts to a brown slag It is soluble ui dilute HC1 
with the evolution of EkS Alabandite occurs with other sulphides at 
Kapnik, Hungary, at Tarma, Peru, at Puebla, Mexico, and m the 
United States at Tombstone, Arizona, and on Snake River, Summit Co , 
Colorado 

Pentlandite ((Fe Ni)S) may belong to this group Iron is frequently 
found in crystallized sphalerite Its sulphide, therefore, may be isomor- 
phous with sphalerite, in \\hich case pentlandite, which is probably an 
isomorphous mixture of NiS and FeS, would also belong m the sphal- 
erite group The mineral occurs in light bronzy yellow, granular masses 
with a distinct octahedral cleavage, a hardness of 3 5-5 and a density of 
46 It is a nonconductor of electricity Pentlandite occurs with 
chalcopynte (CuFeS2) and pyrrhotite (FerSg), at Sudbury, Ontario, 
where it is probably the constituent that furnishes most of the nickel 
(seep 92) 

It is distinguished from pyrrhotite, which it resembles in appearance, 
by its cleavage and the fact that it is not magnetic Moreover, it 
weathers to a brassy yellow color, while pyrrhotite weathers bronze 

WURTZITE DIVISION 

The wurtzite group comprises only two or three members, wurt.iie 
(ZnS), greenoMe (CdS), and possibly pyrrhottte (Fe n S H+1 ) All crys- 
tallize m the holohedral division of the hexagonal system and the first 
two are unquestionably heimmorphic (dihexagonal pyramidal class) 
Pyrrhotite is the most common. 

Wurtzite (ZnS) is one of the dimorphs of ZnS, sphalerite being the 
other. It occurs in brownish black crystals, m masses and m fibers 



SULPHIDES, TELLURIDES, ETC 91 

Its crystals are combinations of ooP(ioib) with 2^(2021) and 
oP(oooi) at one end, and a series of steeper pyramids at the 
other Their axial ratio is i : 8175 The a &gk ion Aoili=4o 9', 

2P(022l) A2P(022I) = 52 2J f 

The mineral is brownish black to brownish yellow and its streak 
is brown Its hardness is between 3 and 4 and its sp gr is about 4 
It conducts electricity very poorly In chemical and physical prop- 
erties it resembles sphalerite Its crystals ha\e been produced by 
fusing a mixture of ZnSO.4, fluonte and barium sulphide They are 
frequently observed as furnace products 

Wurtzite occurs as crystals at the original Butte Mine, Butte, 
Montana, and in a mine near Benzberg, Rhenish Prussia, at both 
places associated \\ith sphalerite They also occur \uth silver ores near 
Oruro and Chocaya, Bolivia, and near Quispisiza, Peru 

Greenockite. Greenockite (CdS) is completely isomorphous with 
wurtzite Its crystals have an axial ratio 
i ' 8109 In general habit they are like 
those of wurtzite but they contain many more 
planes (Fig 36) The angle ioTiAoiTi = 
39 58 Crystals are rare and small The 
mineral usually occurs as a coating on other 
minerals, especially sphalerite Its color is 
honey to orange-yellow, its streak orange- FIG 36 Greenockite Crys- 
yellow, and its luster glassy or resinous It tal OOP, ioT<^(w), aP, 

is transparent or translucent and is brittle 2 ? x ^> ^ IOI JL^ and 
TII j j A i_ F o 001 (c) (The form 

Its hardness is 3-3 5 and density about 4 9 i p> Iol2 (l) ls oft en pres- 

Its index of refraction w=2 688 When ent at the upper end of 

heated in the closed tube it becomes carmine, the crystals ) 

but it changes to its original color on cooling. 

It yields the usual reactions for sulphur and cadmium, and dissolves 

in HC1, yielding H 2 S 

Crystals have been obtained by melting a mixture of CdO, BaS, 
and CaF2, and by heating cadmium in an atmosphere of EfeS to near 
fusing point The mineral is a common furnace product Greenockite 
crystals occur with prenmte at Bishoptown, Scotland, and as coatings 
on sphalerite in the zinc regions of Missouri and Arkansas, and at 
Fnedensville, Pennsylvania, 




92 DESCRIPTIVE MINERALOGY 



Pyrrhotite (Fe n S n +i) 

Pyrrhotite, or magnetic pyrite, occupies the anomalous position 
of being one of the most important ores of nickel, whereas it is essen- 
tially a sulphide of iron The name is really applied to a series of 
compounds whose composition ranges between FesSo and Feu>Si7 
The crystallized material is in some cases FerSs, and in others, FenSi2 
It is probably a solid solution of FeS2 or S in the sulphide of iron (FeS) 
As usually found, pyrrhotite is in bronze-gray granular masses, that 
tarnish rapidly to bronze on exposure to the air Good crystals of 
the mineral are rare. 

Analyses of pyrrhotite vary widely The percentages of Fe and S 
corresponding to FeySs are Fe, 60 4, S, 39 6, and those corresponding 
to FenSi2 are Fe, 61 6, S, 38 4 Much of the mineral contains in addi- 
tion to the iron and sulphur sufficient nickel to render it an ore of this 
metal, but it is probable that the nickel is present in pentlandite (see 
p 90) or some other nickel compound embedded in the pyrrhotite 

Analyses of pyrrhotite from various localities are 

S Fe Co Ni Total 

Schneeberg, Saxony 39 10 6r 77 tr 100 87 

Brewster, NY 37 98 61 84 25 100 07 

Sudbury, Ontario 38 91 56 39 4 66 99 96 

Gap Mine, Penn. 38 59 55 82 5 59 100 oo 

The few crystals of pyrrhotite known are distinctly hexagonal in 
habit with a c=i i 7402 They are com- 
monly tabular or acutely pyramidal, but it 
has not been established that they are hemi- 
morphic, although the almost universal pres- 
ence of FeS in crystals of wurtzite would 
FIG 37 -Pyrrhotite Crystal mdlcate that the two su b sta nces are isomor- 
oP, oooi (c), P, ion (s); , _, ^ , , . f 

4 P, 4041 (), and COP, P hous The tabular crystals possess a broad 
I0 lo (m) basal plane, which surmounts hexagonal prisms 

ooP(ioTo) and oop 2 (ii2o) ; and a series of 

pyramids, of which 2P(2O2i), JP(ioT2), P(ioli) and P2(ri22) are the 
most frequent (Fig 37 ) The angle loli AoiTi = S3 ; 

The cleavage of pyrrhotite is not always equally distinct When 
marked it is parallel to ooP2(ii2o) There is also often a parting 
parallel to the base Its fracture is uneven The mineral is brittle. 
It is opaque, and has a metallic luster Its color varies between bronze- 




SULPHIDES, TELLURIDES, ETC 93 

yellow and copper-red, and its streak is grayish black Its hardness is 
a little less than 4 and its density about 4 5 All specimens are magnetic 
but the magnetism varies greatly in intensity, being at a maximum in 
the direction of the vertical axis The mineral is a good conductor of 
electricity. 

Pyrrhotite gives the usual reactions for iron and sulphur, and some- 
times, in addition, the reactions for cobalt and nickel It is decom- 
posed by hydrochloric acid with the evolution of EbS, which may 
easily be detected by its odor. 

From the many sulphides more or less closely resembling pyrrhotite 
in appearance, this mineral may easily be distinguished by its color 
and density and by its magnetism 

Syntheses Crystals may be obtained by heating iron wire or 
Fes04, or dry FeCk to redness in an atmosphere of dry HoS and by 
heating Fe in a closed tube with a solution cf FcCls saturated with 
H 2 S 

Occurrence, Locd^t^es and Origin Pyrrhotite occurs completely 
filling vein fissures, and also as crystals embedded in other minerals 
constituting veins It occurs also as impregnations in various rocks 
and as a segregation in the coarse-grained basic rock known as nonte, 
where it is believed to have separated from the magma producing the 
rock It may also in some cases be a product of metamorphism on the 
borders of igneous intrusions 

It is found at Andreasberg, Harz, Bodenmais, Bavaria, Minas 
Geraes, Brazil, various points in Norway and Sweden, and on the 
lavas of Vesuvius In North America crystals occur at Standish, Maine, 
at Trumbull, Monroe Co , N Y , and at Elizabethtown, Ontario 
The mineral has been mined at Ducktown, Tenn , at Ely, Vermont, 
and at Gap Mine, Lancaster Co , Penn 

Its mines at present, however, are at Sudbury, in Ontario, where the 
mineral is associated with magnetite, chalcopynte and pentlandite 
((Fe Ni)S) on the lower border of a great mass of igneous rock (norite). 
Besides these there are present also embedded in the pyrrhotite 
small quantities of other minerals, so that the ore as mined is very 
complex. 

Pyrrhotite is sometimes found altered to pyrite, to limomte and to 
siderite (FeC0 3 ) 

Extraction Pyrrhotite is crushed and roasted to drive off the 
greater portion of the sulphur It is then placed in a furnace and 
smelted with coke and quartz The nickel, copper and some of the 
iron, together with some of the fused sulphides, collect as a matte in the 



94 DESCRIPTIVE MINERALOGY 

bottom of the furnace from which it is withdrawn from time to time 
The matte is next roasted to transform the iron it contains into oxides 
and the remaining nickel and copper are separated by patented or secret 
methods 

Uses The mineral is sometimes worked for the sulphur it con- 
tains Its principal use, however, is as a source for nickel, nearly all of 
this metal used in America coming from the nickehferous variety found 
at Sudbury, Ontario 

The metal nickel has come into extensive use in the past few years 
in connection with the manufacture of armor plate for warships The 
addition of a few per cent of nickel to steel hardens it and increases 
its strength and elasticity 

Nickel is also extensively used in mckel-platmg and in the manufac- 
ture of alloys German silver is an alloy of nickel, copper and zinc The 
nickel currency of the United States contains about 25 per cent Ni and 
75 per cent Cu Monel metal is a silver-white alloy containing about 
75 per cent Ni, i per cent Fe and 29 per cent Cu It is stronger than 
ordinary steel, takes a brilliant finish and is impervious to acids It is 
made directly at Sudbury, Ont , by smelting 

Production The production of pyrrhotite and chalcopyrite (CuFeS) 
at the Sudbury mines in 1912 amounted to 737,584 short tons The 
value of the matte produced was $6,303,102, and the value of nickel con- 
tained in it was about $16,000,000 About half of the nickel was used 
in America, the remainder, amounting to $8,515,000, was exported, after 
being refined in the United States Formerly the United States pro- 
duced a considerable quantity of nickel from domestic ores, most of 
it from pyrrhotite, but the mines have been closed down within the past 
few years. It is, however, produced as a by-product in the refining 
of copper ores to the amount of about 325 tons annually, This is worth 
about $260,000 (see also p, 400). 

MILLERITE GROUP 

This group comprises sulphides, arsenides and antimonides of nickel. 
It includes the minerals millmte (NiS),mccohte (NiAs), ante (Ni(Sb As)) 
bwthauptite (NiSb) and a few others Of these only millente and nic- 
colite are at all common The minerals all crystallize m the hexagonal 
system, possibly in the rhombohedral division (ditrigonal scalenohedral 
class). Well defined crystals are, however, rare and often capillary so 
that their symmetry has not been determined with certainty. 



SULPHIDES, TELLURIDES, ETC 95 



Mfflerite (NiS) 

Millerite is easily recognized by its brass-yellow color It occurs 
most frequently in slender hair-like needles, often aggregated into tufts 
or radial groups, or, woven together like wads of hair, forming coatings 
on other minerals 

Pure millente contains 35 3 per cent sulphur and 64.6 per cent nickel 
It frequently contains also a little Co and Fe. 

Crystals are thin, acicular or columnar with prismatic and rhom- 
bohedral faces predominating, and an axial ratio of i 330, or of i : 9886 
if the rhombohedron 311(0331) is taken as the ground form 

The mineral is elastic Its hardness is 3-3 5 and density about 5 5. 
It is opaque and brassy yellow Its streak is greenish black. It is an 
excellent conductor of electricity 

The mineral yields sulphurous fumes in the open tube. After roast- 
ing it gives, with borax and microcosmic salt, a violet bead when heated 
in the oxidizing flame of the blowpipe On charcoal with NaaCOs it 
yields a magnetic globule 

Synthesis Bunches of yellow acicular crystals of N1S have been 
formed by treatment of a solution of NiSO^ with H^S, under pressure. 

Localities Millerite occurs as long acicular crystals in cavities in 
other minerals at Joachimthal, in Bohemia, and at many places in 
Saxony In the United States it forms radiating groups in cavities in 
hematite (F&Os) at Antwerp, NY At the Gap Mine, Lancaster Co , 
Penn , it forms coatings on other minerals and at St Louis, Mo and 
at Milwaukee, Wis , it occurs in delicate tangled tufts in geodes in lime- 
stone, Nowhere does it occur in sufficient quantity to constitute an ore. 

Niccolite (NiAs) 

Niccolite usually occurs massive, though crystals are known It is 
of economic importance only in a few localities 

Theoretically, the mineral contains 56 10 per cent As and 43 90 per 
cent Ni, but as usually found it contains also Sb, S, Fe and often small 
quantities of Co, Cu, Pb and Bi 

Its crystals, which are rare, are hexagonal and hemimorphic (prob- 
ably dihexagonal pyramidal class), with a : c=i : 8194 The prism 
ooP(ioTo), and oP(oooi) are the predominant forms, with the 
pyramids P(ioTi) and ^(5057) less well developed The angle 



The mineral is pale copper-red and opaque It has a brownish 



96 DESCRIPTIVE MINERALOGY 

black streak. Its hardness is about 5 and its density 7 6 The surfaces 
of nearly all specimens are tarnished with a grayish coating The min- 
eral is a good conductor of electricity 

In the open tube mccohte yields arsenic fumes and often traces of 
862 On charcoal with Na2COs it yields a metallic globule of nickel 
It dissolves in HNOs with the precipitation of AsgOa The apple-green 
solution, thus produced, becomes sapphire-blue on addition of ammonia 

Its peculiar light pink color and its reactions for arsenic and nickel 
distinguish mccohte from all other minerals, except, perhaps, breit- 
kaupttte, which, however, contains antimony 

Occurrence Niccohte occurs principally in veins in crystalline 
schists and in metamorphosed sedimentary rocks, associated with silver 
and cobalt sulphides and arsenides 

Local^foes The principal locality for mccohte in North America is 
Cobalt, Ontario, where it is found with native silver and silver, cobalt, 
and other nickel compounds, all of which are thought to have been de- 
posited by hot waters emanating from a mass of diabase In Europe it 
is abundant at Joachimsthal in Bohemia, and at a number of other 
places in small quantity 

Although rich in nickel, the mineral is not used as an ore at present, 
except to a very minor extent, most of the nickel of commerce being 
obtained from other compounds (see p 94) 

Breithauptite (NiSb) is rare It is of a light copper-red color, much 
brighter than that of mccohte, and its streak is reddish brown Its hard- 
ness is 5 5 and density about 7 9 Its crystals are hexagonal tables 
with an axial ratio i i 294, and a distinct cleavage parallel to oP(ooi) 
It usually occurs m dendritic groups, m foliated and finely granular 
aggregates and in dense masses It is a frequent furnace product, when 
ores containing Ni and Sb are smelted It is found at Andreasberg, Harz , 
at Sarrabus, m Sardinia, at Cobalt, Ont , and at a few other places It 
is distinguished from mccohte by its deeper color and its content of Sb. 



Covelhte (CuS) 

Covellite, or indigo copper, is the cupric sulphide, chalcocite being 
the corresponding cuprous salt It is called indigo copper because of 
the deep blue color of its fresh fracture. It is often mixed with other 
copper compounds from which it has been derived by alteration It 
usually occurs massive, but crystals are known It is an unimportant 
ore of copper. 



SULPHIDES, TELLURIDES, ETC 97 

The theoretical composition of the mineral is 33 56 per cent S, 
66 44 per cent Cu It usually, however, contains also a little iron and 
often traces of lead and silver 

Crystals of covellite are not common. They are hexagonal \\ith 
a c-i 3 972 and their habit is usually tabular The forms observed 
are oP(oooi), oo P(iolo), P(ioTi) and JP(ioT4) icTi /\oi Ti = 77 42'. 

The mineral has one perfect cleavage parallel to oP(oooi) In 
thin splinters it is flexible Its hardness is i 5-2 and density about 
4 6 Its color is dark blue and its streak lead-gray to black It is 
opaque, with a luster that is sometimes nearly metallic, but more 
frequently dull It is a good electrical conductor 

The blowpipe reactions of covellite are like those of chalcocite, with 
these exceptions Covellite burns ^ith a blue flame when heated on 
charcoal, and yields a sublimate of sulphur in the closed tube 

Covellite is distinguished from other minerals than chalcocite by 
its reactions for Cu and S and the absence of reactions for Fe. It is 
distinguished from chalcocite by its color and density and by the fact 
that it ignites on charcoal 

Syntheses The treatment of green copper carbonate with water 
and EkS in a closed tube at 8o-9o yields small grains of covellite 
The mineral has also been produced by the action of HsS upon vapor 
of CuCl2, and by treating sphalerite with a solution of copper sulphate 
in a sealed glass tube containing C02 at a temperature of iso-i6o 
for two days 

Localities and Origin The mineral is comparatively rare It is 
abundant in Chile and Bolivia and at Butte, Mont , and is found in 
crystals on the lava of Vesuvius and elsewhere It usually occurs as 
an alteration product of other copper-sulphur compounds, especially in 
the zone of secondary enrichment of copper veins 

Uses It is mined with other compounds and used as a source 
of copper, 

CINNABAR GROUP 

This group comprises sulphides, selenides and tellundes of mercury 
The group is dimorphous, with its members crystallizing in henuhedrons 
of the isometric system (hextetrahedral class) and in tetartohedrons 
of the hexagonal system (trigonal trapezohedral class) The isometric 
HgS is known as metacmnabante and the hexagonal form as cinnabar 
Only the latter is important In addition to these are known the rare 
compounds onofnte (Hg(S Se)), tiemanmte (HgSe) and coloradcnte 
(HgTe), all of which are isometric 



98 



DESCRIPTIVE MINERALOGY 



Cinnabar (HgS) 

Cinnabar is the only compound of mercury that occurs in sufficient 
quantity to constitute an important ore Nearly all of the mercury, 
or quicksilver, in the world is obtained from it The mineral occurs 
both crystallized and massive The ore is a red crystalline mass that 
is easily distinguished from all other red minerals by its peculiar shade of 
color and its great weight. 

Theoretically, it contains 13 8 per cent S and 86 2 per cent Hg 
Massive cinnabar is, however, usually impure through the admixture 
of clay, iron oxides or bituminous substances Occasionally the quan- 
tity of organic material present is so large that the mixture is inflam- 
mable. 

Though cinnabar is usually granular, massive or earthy, it some- 
times occurs beautifully crystallized 
in small complex and highly modi- 
fied hexagonal crystals that exhibit 
tetartohedral forms (trigonal trape- 
zohedral class) Usually the crys- 
tals are rhombohedral or prismatic 
m habit Their axial ratio is 
i . i 1453 Planes belonging to 
more than 100 distinct forms have 
been observed, but the crystals on 
which they occur aie usually so 
small that few of them are of im- 
portance as distinguishing charac- 
teristics. The prismatic crystals, which are the most common in 
this country, are often bounded by ooR, (rolo) and R, (4045) 
(Fig 38) Others, however, are very complicated Their cleavage is 
perfect parallel to oo R(ioTo). 

The mineral is slightly sectile It is transparent, translucent or 
opaque, is of a cochineal-red color, often inclining to brown, and its 
streak is scarlet Its hardness is only 2-2 5 and its density about 
8 i It is circularly polarizing and is a nonconductor of electricity 
Its dimorph, metacinnabante, on the other hand, is a good conductor 
The indices of refraction of cinnabar are co= 2 854, ==3 201 

When heated gently in the open tube cinnabar yields sulphurous 
fumes and globules of mercury. On charcoal before the blowpipe it 
volatilizes completely. 

There are only a few minerals with which cinnabar is likely to be 




FIG 38 -Cinnabar Crystals with R, 
iolo (m), fR, 4045 (0, R, 2025 
(/), R, loTi (0 and o&, oooi (c) 



SULPHIDES, TELLURIDES ETC 99 

confused, since its color and streak are so characteristic From all 
red minerals but realgar it may easily be distinguished by its sulphur 
reaction From realgar it is distinguished by its great density and its 
greater hardness 

Pseudomorphs of cinnabar after stibnite, dolomite ((Ca Mg)COsJ, 
pynte and tetrahednte (a complicated sulpho-salt) have been described 

Synthesis Crystals ha\ e been made b> heating mercury in an aque- 
ous solution of HbS 

Occurrence Localities and On gin Cinnabar is usually found in 
veins cutting serpentine, limestones, slates, shales and \anous schists 
It is associated \Mth gold, various sulphides, especially pynte and mar- 
casite (FeS 2 ) calcite (CaCOs), barite (BaSO-i), fluonte (CaF 2 ) and 
quartz It is also found impregnating sandstones and other sedimen- 
tary rocks, and sometimes as a deposit from hot springs Its deposi- 
tion is thought to be the result of precipitation from ascending hot 



Crystallized cinnabar occurs at a number of places in Bohemia, 
Hungary, Serbia, Austria, Spam, California, Texas, Nevada, and at 
ether localities m Europe Asia and South America 

The principal deposits of economic importance are at Almaden 
in Spain, at Idria in the Province of Carmola, Austria, at Bakhmut 
in southern Russia, at various points along the Coast Ranges in Cal- 
ifornia, in Esmeralda, Humboldt, Nye and Washoe Counties in Nevada, 
at many points in Oregon and Utah, and at Terhngua in Texas The 
mineral is also abundant in Peru and in China but in these countries 
it has not yet been mined profitably The California cinnabar district 
extends for many miles along the Coast Ranges, but at only about a 
dozen places is the mineral mined 

The Spanish mines, near the city of Cordova, have been worked 
for many hundreds of years Much of the ore is an impregnation of 
sandstone and quartzite the mineral sometimes comprising as much 
as 20 per cent of the rock mined 

Extraction The metallurgy of cinnabar is exceedingly simple It 
consists simply in roasting the ore alone, or mixed with limestone, and 
conducting the fumes into a condensing chamber that is kept cool. 
The sulphur gases are allowed to escape through the chamber in which 
the mercury is collected 

Uses of Metal Mercury finds many uses in the arts Its most im- 
portant one is in the extraction of gold and silver by the amalgamation 
process It is the essential constituent of the pigment vermilion, which 
is a manufactured HgS. In its metallic state it is largely employed in 



100 DESCRIPTIVE MINERALOGY 

the making of mirrors, of barometers, thermometers and other physical 
instruments Some of the salts are important medicinal preparations 
while others are used in the manufacture of percussion caps 

Production The world's annual production of quicksilver, all of 
which is obtained from cinnabar, is not far from 4,000 metric tons The 
United States produced 940 tons in 1912, valued at $1,053,941 Of this 
total California yielded 20,524 flasks of 75 Ibs each, valued at about 
$863,034, and Texas and Nevada 4,540 flasks valued at $190,907 To 
produce these quantities of metal California mined I39>347 tons of ore 
and Texas and Nevada 16,346 tons The California ore yielded n Ibs 
of metal per ton and the Nevada and Texas ore 20,8 Ibs, 

Metacmnabarite (HgS) is generally found as a gray-black massive 
mineral with a black streak It is brittle, has a hardness of 3 and a 
density of 7 8 It is associated with cinnabar at some of the mines in 
California and Mexico, and at a few places in other countries It is 
exceedingly rare. 

THE METALLIC DISULPHIDES, DISELENIDES AND DIARSENIDES 

The disulphides, diselemdes, ditellundes, diarsemdes and dianti- 
monides differ from the corresponding monocompounds m that they 
contain double the quantity of S, Se, Te and Sb They are divisible 
into two groups, one of which comprises sulphides, arsenides and anti- 
monides of iron, manganese, cobalt, nickel and platinum, and the other 
the tellundes and selemdes of gold and silver, 

GLANZ GROUP 

The glanz group is an excellent illustration of an isodimorphous group. 
Its members are characterized by their hardness, opaqueness, light color 
and brilliant luster. Hence the name of the group In composition 
the minerals belonging to the group are sulphides, arsenides or anti- 
momdes of the iron-platinum group of metals, with the general formula 
RQ2 in which R is Mn, Fe, Ni, Co, Pt, and Q=S, As and Sb The com- 
position of the more simple members may be represented by the formula 

/S 
Fe/ | , and of those in which arsenic or antimony replaces a part of the 

<As=As\ 
>Fe. 
S y 

It is probable, however, that some of the cobalt and nickel arsenides 



SULPHIDES, TELLURIDES, ETC 101 

are mixtures and that their indicated compositions are only approximate 
All members of the group are believed to be dimorphous, crystallizing 
in the isometric (dyakisdodecahedral class), and in the orthorhombic 
systems (orthorhombic bipyramidal class), though not all have as yet 
been found in both forms The most important members of the group, as 
at present constituted, are as follows 

Isometric Orthorhombic 

Pynte FeSg Marcasite 

Hauente MnS2 

FeAsS Arsenopyrite 

FeAs2 Lolhngite 

CobalMe CoAsS Glaucodot 

Gersdor/tte (Ni Fe)AsS 

Korymte (Ni Fe)(As Sb S) 2 Wolfachite 

Ullmamte NiSbS 

Smdtite CoAs 2 Safflonte 

Ckloanthite NiAs 2 Rammdsbergite 

Sperryhte PtAs 2 

The group is divided into two subgroups, the regularly crystallizing 
minerals forming the pynte group and the orthorhombic ones the mar- 
casite group The most important members of the former group are 
pynte, cobaltite, smaltite and chloanthite The most important members 
of the marcasite group are marcastte, arsenopynte and lolhngite. 



PYRITE 

The crystallization of the pyrite group is in the parallel heimhedral 
division (dyakisdodecahedral class) of the isometric system. The 

occurrence of the form - , 210, is so frequently seen on the mineral 

pyrite that it has received the name pyritoid 

The group is so perfectly isomorphous that a description of the forms 
on one member is practically a description of the forms on all. 

Pynte (FcS 2 ) 

Pyrite, one of the most common of all minerals, is found under a 
great variety of conditions as crystals, as crystalline aggregates and 
as crystalline masses It occurs under practically all conditions and in 
all situations It is easily recognized by its bright yellow color, its 
brilliant luster and its hardness, 



102 



DESCRIPTIVE MINERALOGY 



Pyrite containing, theoretically, 46 6 per cent of iron and 53 4 per 
cent of sulphur is usually contaminated with small quantities of nickel, 




FTC 39 Group of Pyrite Crystals in which the Cube Predominate The c 

/20oo\ 
are striated parallel to the edge between oo oo (100) and I ) , (210) 



cobalt, thallium and other elements An auriferous variety is worked 
for gold, yielding in the aggregate a large quantity of the precious 






FIG 40 IK, 4 i 

FIG 40 Pynte Crystals on which (in) Predon mates o=0, n i and c 

210 
FIG 41 Pynte Crystal with oo 02, 210 (e) and 0, in (a) 



metal Sometimes arsenic is present in small quantity Analysis of 
the crystals from French Creek, Penn , gave 



8=5408, As=o 20, Fe=44 24, Co=i 75, Ni=o 18, Cu=oos, =100 50. 



SULPHIDES, TELLURIDE3, ETC 



103 



The number of forms that have been observed on pynte crystals is 

very large Hintze records 86 The cube and the pyntoid ^-^ I 

L 2 J 




FIG 42 Group of Pynte Crystals in \\hich ooQ2 (210) Predominates 
Daly- Judge Mine, near Park City, Utah (After J W Bmtfaett ) 



From 



(210) are the most common of these, though the octahedron and the 

dodecahedron are not rare Four distinct types of crystals may be 

recognized, viz those with the cubic (Fig 39), 

the octahedral (Fig. 40), and the pyntoid 

habits (Figs 41 and 42), and those that are 

interpenetrating twins (Fig 43) The cubic 

and the pyritoid planes are often striated 

parallel to the edges between these faces The 

interpenetrating twins are twinned about the 

plane 0(ni) 

The cleavage of pynte is imperfect and 
its fracture conchoidal. The mineral is 
brittle Its hardness is 6-6 5 and density 
about 5. Its luster is very brilliant and 
metallic Its color is brassy yellow and its 

streak greenish or brownish black With steel it strikes fire, hence its 
name from the Greek word meaning fire. It is a good conductor of 
electricity and is strongly thermo-electric. 




FIG 43 Pynte Interpene- 
trationTwin Two Pyn- 
toids ( s Os, 210) Twinned 
about O in 



In the closed tube pynte yields a sublimate of sulphur and a residue 
that is magnetic On charcoal sulphur is freed This burns with the 
blue flame characteristic of the substance The globule remaining after 
heating for some time is magnetic Treated with nitric acid the 
mineral dissolves leaving a flocculent residue of sulphur, which when 
dried and heated may readily be ignited 

Pynte in some of its forms so closely resembles gold that it is often 
known as fool's gold There is, of course, no difficulty in distinguishing 
between the two metals, since pyrite contains sulphur and is soluble in 
nitric acid, while gold contains no sulphur and is insoluble in all simple 
acids. 

The mineral is most easily confounded with chako pynte (CuFeS>), 
though the difference in hardness of the two easily serves to distinguish 
them Chalcopynte may be readily scratched with a knife blade or a 
file, while pyrite resists both The latter mineral, moreover, contains 
no copper 

Syntheses Small crystals of pyrite are produced by the action 
of HaS on the oxides or the carbonate of iron enclosed in a sealed tube 
heated to 8o-9o, also by the passage of EbS and FeCla vapors through 
a red-hot porcelain tube. 

Occurrence and Origin Pynte occurs in veins and as grains or 
crystals embedded in all kinds of rocks. In rocks it usually appears as 
crystals, but in vein-masses it may appear either as crystals, with other 
minerals, or as radiating or structureless masses occupying entirely the 
vein fissures In slates it often occurs in spheroidal nodules and 
concretions of various forms, and also as embedded crystals. The 
mineral is the product of igneous, metamorphic and aqueous agencies 

Pyrite weathers readily to hmonite. In ore bodies near the 
surface it is oxidized. A portion of the mineral changes to FeSQt 
which percolates downward and aids in the concentration of any 
valuable metals that may be present m small quantity in the ore. 
Another portion of the iron remains near the surface in the form of 
lunonite This covering of oxidized material is known as the " gossan " 
and it is characteristic of all pyrite deposits 

Localities Pynte crystals are so widely distributed that but very 
few of its most important occurrences may be mentioned here In the 
mines of Cornwall, Eng , and in those on the Island of Elba very large 
crystals are found Fine crystals also come from many different places 
in Bohemia, Hungary, Saxony, Peru, Norway, and Sweden 

In the United States the finest crystals are at Schoharie and Rossie, 
N Y ; at the French Creek mines in Chester Co , and at Cornwall, 



SULPHIDES, TELLURIDE3, ETC 105 

Lebanon Co , Penn , and near Greensboro and Guilford Co , X Carolina 
Massive pyrite occurs in great deposits at the Rio Tmto mines in 
Spain, at Rowe, Mass , in St Lawrence and Ulster counties, X Y , 
in Louise Co , Va , and in Pauldmg Co , Ga Much of the massive 
pynte in the veins of Colorado, California and of the southern states, 
from Virginia to Alabama, is auriferous and much of it is mined for the 
gold it contains 

Uses Pynte is used principally in the manufacture of sulphuric 
acid The mineral is burned in furnaces and the 862 gases thus result- 
ing are carried to condensers \\here they are oxidized by fineh divided 
platinum or by the oxides of nitrogen The residue, which consists 
largely of Fe20s, is sometimes smelted for iron or made into paint 
This residue also contains the gold and other \aluable metals that may 
have been in the original pyrite. 

The sulphuric acid obtained from pyrite enters into many manu- 
facturing processes The greater portion of it is consumed in the 
artificial fertilizer industry 

Production Pyrite is mined in the United States in Franklin Co , 
Mass , in Alameda and Shasta Counties, California, in Louisa, Pulaski 
and Prince William Counties, Va , in Carroll Co , Ga 3 in St Lawrence 
Co , N Y , m Clay Co , Alabama, and at the coal mines in Ohio. 
Illinois and Indiana where it is a by-product The total production 
of the United States in 1912, amounting to 330,928 long tons, was 
\alued at $1,334,259 Virginia is by far the largest producer In 
addition to this quantity the trade consumed 970,785 tons of imported 
ore, most of which came from Spain, and utilized the equivalent of 
260,000 tons of pynte m the shape of low grade sulphide copper ores 
from Ducktown, Tenn , and zinc sulphide concentrates from the Mis- 
sissippi Valley and elsewhere for the manufacture of sulphuric acid. 
The total amount of sulphuric acid manufactured in the United States 
during 1912 was 2,340,000 short tons, valued at $18,338,019 The total 
world production of pyrite is about 2,000,000 tons annually 

Small quantities of the mineral are also mined for local consumption 
in Lumpkin Co , Georgia, and near Hot Springs, Arkansas Much 
aunferous pynte has also been mined in the southern states and the 
Rocky Mountain region for the gold it contains This metal is sepa- 
rated from the pyrite partly by crushing and amalgamation and partly 
by smelting or by leaching processes. In the former case the gold 
occurs as inclusions of the metal in the pynte. 



106 DESCRIPTIVE MINERALOGY 

Cobaltite (CoAsS) 

Cobaltite is a alver-nvhite or steel-gray mineral occurring in massive 
forms or in distinct crystals exhibiting beautifully their hemihedral 
character It is completely isomorphous with the corresponding nickel 
compound, gersdorffite (NiAsS), and consequently mixtures of the 
two are common 

Cobaltite usually contains some iron and often a little nickel 
Theoretically, it consists of 19 3 per cent S, 45 2 per cent As and 35 5 
Co The compositions of a massive variety from Siegcn, Westphalia, 
and that of crystals from Nordmark, Norway, are as follows 

As S Co Fe Ni Total 

Siegen 45 31 19 35 33 71 i 63 100 oo 

Nordmark 44 77 20 23 29 17 4 72 i 68 100 57 

The crystallization of cobaltite is perfectly isomorphous with that 
of pyrite, though the number of its forms observed is far smaller The 

most common planes are those of oo oo (100) , 0(i 1 1 ) and (210) 

The cleavage of cobalt is fairly good parallel to oo oo (100) Its 
fracture is uneven, its hardness is 5 5 and its density about 6 2 The color 
of the mineral, as stated above, varies between silver-white and steel- 
gray Its streak is grayish black It is a good conductor of electricity 

In the open tube cobaltite reacts for S and As On charcoal it 
yields a magnetic globule which when fused with borax on platinum 
wire yields a deep blue bead It weathers fairly readily to the rose- 
colored cobalt arsenate known as erythnte (Coa(As04)2 SEfeO) 

By its crystallization and color cobaltite is distinguished from 
nearly all other minerals but those of the same group From most of 
these it is easily distinguished by its blowpipe reactions foi sulphur, 
arsenic and cobalt 

Occurrence and Origin Cobaltite occurs mainly m veins that are 
believed to have been filled by upward moving solutions emanating 
from igneous rocks It is associated with compounds of nickel and other 
cobalt compounds and with silver and copper ores 

Localities Cobaltite is not very widely distributed Large, hand- 
some crystals occur at Tunaberg in Sweden, at Nordmark, Norway, 
at Siegen, Westphalia, and near St Just in Cornwall, England It is 
found also in large quantity at Cobalt, Ontario, associated with silver 
ores and nickel compounds 



SULPHIDES, TELLURIDES ETC 107 

Uses Cobaltite is said to be used b\ jewelers in India in the pro- 
duction of a blue enamel on gold ornaments It is employed also in the 
manufacture of blue and green pigments and in the manufacture of com- 
pounds used in small quantity in the various arts Smalt is the most 
valuable of the cobalt pigments and is at present the chief commercial 
compound of this metal It is a deep blue glass that cheers from 
ordinary glass in containing cobalt in place of calcium Smalt is made 
from cobaltite and from other cobalt ores b\ fusion \\ith a mixture of 
quartz and potassium carbonate Certain cobalt compounds are sug- 
gested as excellent driers for oils and varnishes The mineral is also 
utilized as an ore of cobalt, \\hich in the form of stelhte, an alloy com- 
posed of 70 per cent cobalt, 15 per cent chromium and 15 per cent 
molybdenum or tungsten, bids fair to acquire a large use as a material 
for the manufacture of table cutlery and edged tools The use of the 
metal has also been suggested as a material for coinage in place of 
nickel. 

Production Most of the cobalt of commerce is handled by the 
trade in the form of the oxide It is produced from the \ anous cobalt 
minerals, mainly as a by-product in the extraction of nickel, and hence 
ver> little is obtained from ccbaltite The mines at Cobalt, however, 
have furnished a large quantity of cobaltite and smaltite \uthin the past 
few years and these have gone into the manufacture of the oxide, of 
uhich about 515 tons -\\ere produced in 1912, ha\mg a \alue of 
$317,165 

Smaltite (CoAs>) 

Smaltite is another important ore of cobalt It is found in crystals 
and masses 

Its theoretical composition is 71 88 per cent As and 28 12 per cent 
Co, though it usually contains also S, Ni, Fe and frequently traces of 
Bi, Cu and Pb Since it is isomorphous \uth the arsenide of nickel 
chloanthite (NiAs2), mixed crystals of the t\\o are common Moreover, 
sharply defined crystals have been found to consist of mechanical mix- 
tures of several compounds 

Smaltite occurs in small crystals of cubical habit with ooOoo (100), 
0(in) and various pyritoids predominating 

The mineral is tin-white to steel-gray, and opaque, and has a grayish 
black streak It is often covered ^ith an iridescent or a gray tarnish. 
Its cleavage is indistinct, its fracture uneven, its hardness 5-6 and 
density 6 3-7 It is a good electrical conductor 

Before tie blowpipe on charcoal smaltite yields arsenic fumes and a 



108 DESCRIPTIVE MINERALOGY 

magnetic globule of metallic cobalt It is soluble in HNOs, yielding a 
rose-colored solution and a precipitate of As2Os 

The mineral is fairly easily distinguished from most other minerals 
by its color and blowpipe reactions From cobaltite it is distinguished by 
the lack of S From a few others that are not described in this volume 
it can be distinguished by its crystallization or by quantitatn e analysis 

Synthesis Smaltite crystals are produced when hydrogen acts at a 
high temperature upon a mature of the chlorides of cobalt and arsenic 

Occurrence and Ongm Smaltite is found associated with cobaltite 
in nearly all of its occurrences It is especially abundant at Cobalt, Out 
As in the case of most other cobalt minerals, its presence is indicated by 
deposits of rose-colored erythnte which coat its surfaces wherever these 
are exposed to moist air Its methods of occurrence, origin and uses 
are the same as for cobaltite (p 107). 

Chloantfaite (NiAso) resembles smaltite in most of its characteris- 
tics The two minerals grade into each other through isomorphous 
mixtures Those mixtures in which the cobalt arsenide is in excess 
are known as smaltite, while those in which NiAs predominates arc 
called chloanthite The pure chloanthite molecule is Ni= 28 i per cent, 
As =7 1 9 per cent 

The two minerals can be distinguished when unmixed with one 
another by the blowpipe reactions for Co and Ni In mixed ciysUis 
the predominance of one or the other arsenides can be determined only 
by quantitative analysis 

Chloanthite containing much iron is distinguished as thathamite, 
from Chatham, Conn , where it occurs with arsenopynte and niccohte in 
a mica-slate 

The mode of occurrence of chloanthite and the localities at which 
it is found are the same as in the case of smaltite. 

Spenyhte (PtAs 2 ) 

Sperryhte is extremely rare It is referred to here because it is the 
only platinum compound occurring as a mineral Chemically, it is 
43 S3 P er cent As and 56 47 per cent Pt, but it contains also small quan- 
tities of Sb, Pd and Fe 

Its crystals are simple They contain only 0(iu), ooOoo(ioo), 
oo 0(no) and several pyntoids Their habit is usually octahedral or 
cubical 

The mineral is opaque and tin-white, and its streak black Its hard- 
ness is 6-7 and density 10 6 



SULPHIDES, TELLURIDE3, ETC 109 

In the closed glass tube it remains unchanged, but in the open tube 
it gives a sublimate of As^Os When dropped upon red-hot platinum 
foil it immediately melts, giving rise to fumes of As20s, and forming 
blisters on the foil that are not distinguishable from the original platinum 
in color or general character It is shnvh soluble in concentrated HC1 
and aqua regia 

Synthesis The mineral has been produced by leading arsenic fumes 
over red-hot platinum in an atmosphere of h\drogen 

Occurrence and Localities Sperrylite occurs as little crystals com- 
pletely embedded in the chalcopynte (CuFeSo) and the gossan of a 
nickel mine, and in the chalcop\nte of a gold-quartz vein near Sudbury, 
Ontario, in covelhte at the Rambler Mine, Encampment, \V\ormng, 
and as flakes in the sands of streams in the Co\\ee Valle\ , Macon Co , Ga 
The flakes resemble very close,!} native platinum, from which they are 
of course, easily distinguished by the test for arsenic 

Uses The sperryhte from Sudbury and \V} ommg furnish much of 
the platinum produced in the United States (see p 64) 

MARCASITE Dl\ ISIOX 

Three members of the marcasite group are important, all are inter- 
esting from the fact that they are so alike in their cr\stalhzation that a 
description of the forms belonging to any one of them might serve as a 
description of those belonging to all others The crystallization of the 
group is orthorhombic (rhombic bipyramidal class), with an axial ratio 
approximately a b ' c= 7 1:12 

Marcasite (FeS 2 ) 

Marcasite, the dimorph of pynte, resembles this mineral so closely 
that in massive specimens it is difficult to distinguish between the two 
They are nearly alike in hardness, in color and in chemical properties 
Marcasite is a little lighter m color than pynte Its density is less 
(about 4 9), and it possesses a greater tendency to tarnish on exposed 
surfaces 

This tarnish indicates that the mineral is more susceptible to altera- 
tion than is pynte One of the products of this alteration is ferrous sul- 
phate, which may often be detected by its taste upon touching the tongue 
to specimens of the mineral In crystallized specimens there is not the 
least difficulty in distinguishing between them, suice their crystallization 
is very different 

Marcasite is orthorhombic (rhombic bipyramidal class), with the 



110 



DESCRIPTIVE MINERALOGY 



axial ratio 7662 i i 2342 Its simple crystals often possess a tabular 
or a pyramidal habit (Figs 44 and 45) In the former case oP(ooi) is 
the predominant face, and m the latter case the two domes P 60 (101) 






FIG 44 FIG 45 

FIG 44 Marcasite Crystal with oP,no(w), oP,ooi(c), P^o , on (/) and JPS5 , 

013 (T) 

FIG 45 Marcasite Crystal with Forms as Indicated in Fig 44, and P M , 101 (e) 

and P, in (s) 

andP <56 (on) The other forms observed on most crystals are oo P(iio), 
P(III), and often |P oo (013) 

Twins are very common, with oo P(no) the twinning plane (Fig 46) 
Sometimes these are aggregated by repeated twinning into serrated 
groups known as cockscomb twins or spearhead twins (Fig 47), because 





FIG 46 FIG 47 

FIG 46 Twin of Marcasite about oo P(iio) 

FIG 47 Spearhead Group of Marcasite Fourling Twinned about no and then 

about i To 

of the outlines of their edges. In many instances the crystals aie acic- 
ular or columnar in habit, forming radiating groups with globular, rem- 
form and stalactitic shapes Concretions are also common The basal 
plane is usually striated parallel to the edge between it and P oo (on) 
The cleavage is distinct parallel to oo P(iio) The fracture is uneven 



SULPHIDES, TELLURIDES, ETC. Ill 

When powdered marcasite is treated \\ith cold nitric acid and 
allowed to stand, it decomposes \uth the separation of sulphur 

Marcasite readih alters to limonite The fact that pyrite, sphaler- 
ite, chalcopyrite, and other minerals form pseudomorphs after it 
indicates that, under suitable conditions, it alters also to these com- 
pounds The mineral is in most cases a direct result of precipitation 
from hot solutions 

Synthesis Marcasite crystals ha\e been prepared by the reduction 
of FeSQi by charcoal in an atmosphere of EfeS 

Occurrence ani Uses The mineral, like pyrite, is found embedded 
in rocks in the form of crystals and concretions, and also as the 
gangue masses of veins It constitutes nearly the entire filling of some 
veins, and forms druses on the walls of cavities in both rocks and miner- 
als It also replaces the organic matter of fossils preserving their shapes 
thus producing true pseudomorphs 

When associated \\ith pyrite it is mined together \\ith this mineral 
as a source of sulphur 

Localities Crystalline marcasite occurs m such great quantity 
near Carlsbad m Bohemia that it is mined The cockscomb variety is 
found in Derbyshire, England, and crystals at Schemmtz in Hungary 
and at Andreasberg and other places in the Harz In the United States 
the mineral occurs as crystals at a great number of places, being par- 
ticularly abundant m the lead and zinc localities of the Mississippi 
Valley, where it sometimes forms stalactites The stalactites from 
Galena, 111 , often consist of concentric layers of sphalerite, galena and 
crystallized marcasite 

Arsenopyrite (FeAsS) 

Arsenopyrite, or mispickel, is the most important ore of arsenic 
It is found in crystals and in compact and granular masses. It is a 
silver-white metallic mineral resembling very closely cobaltite in its 
general appearance 

The formula FeAsS for arsenopynte is based on analyses like the 
following. 

As S Fe Total 

Specimen from Hohenstein, Saxony 45 62 19 76 34 64 100 02 
Specimen from Mte Chalanches, France 45 78 ig 56 34 64 99 98 

Theoretically, the mineral consists of its components m the following 
proportions, As 46 per cent, S 19 7 per cent, Fe 34 3 per cent In many 
specimens the iron is replaced in part by cobalt, nickel or manganese. 



112 



DESCRIPTIVE MINERALOGY 





Sometimes the cobalt is present in such large quantity that the mineral 
is smelted as an ore of this metal 

The axial ratio of arsenopynte is 6773 i i 1882 Its crystals are 
usually simpler than those of marcasite (Fig 48), though the number of 
planes observed in the species is larger. Most of the untwmned crystals 

are a combination of oo P(no) 
with JP66 (014), or P 06 (on), 
or POO(IOI), and have a pris- 
matic habit. Twins are not 
rare The twinning plane is 
the same as in marcasite, 
and repetition is often met 
with The angle no/\i"io= 
68 13' 

FIG 48-Arsenopynte Crystals with cop, The brachydomes are stri- 
no (m) , iP oo , 014 (M), and P 5 , on (j) ated horizontally, and often 

the planes ooP(no) are stri- 
ated parallel to the edge oo P(no) A? *> (101) 

The cleavage of arsenopynte is quite perfect parallel to ooP(no) 
The mineral is brittle and its fracture uneven Its hardness is 5 5-6 
and density about 6 2 Its color is silver-white to steel-gray, its streak 
grayish black It is a good conductor of electricity 

In the closed tube arsenopynte at first gives a red sublimate of AsS 
and then a black mirror of arsenic On charcoal it gives the usual 
reactions for sulphur and arsenic Cobaltiferous varieties react for 
cobalt with borax. The mineral yields sparks when struck wilh. steel 
and emits an arsenic smell It dissolves m nitric acid with the separa- 
tion of sulphur 

Arsenopynte is distinguished from the cobalt sulphides and arsenides 
by the absence of Co 

Synthesis Crystals of the mineral are produced by heating in a 
closed tube at 300 precipitated FeAsS in a solution of NaHCO* 

Occurrence Arsenopynte crystals are often found disseminated 
through crystalline rocks, and often embedded m the gangue minerals of 
veins Like pyrite and marcasite they frequently fill vein fissures. Its 
associates are silver, tin and lead ores, chalcopyrite, pynte and sphalerite 
Localities The mineral is abundant at Freiberg, m Saxony, at 
Tunaberg, in Sweden, and at Inquisivi Mt , Sorato, m Bolivia 

It also occurs in fine crystals at Francoma in New Hampshire, at 
Blue Hill m Maine, at Chatham in Connecticut, and at St. Francois, 
Beauce Co, Quebec Massive arsenopynte is found near Kecscville 



SULPHIDES, TELLURIDES ETC 113 

Essex Co , near Edenville, Orange Co , and near Carmel, Putnam Co , 
N Y , and at Re\\ald, Flo\d Co , Va In most cases it is appaiently 
a result of pneumatoh sis 

Uses Arsenopynte was formerly the source of nearly all the arsenic 
of commerce The mineral is concentrated b\ mechanical methods, and 
the concentrates are heated in retorts, when the following reaction takes 
place FeAsS = FeS+As The arsenic being volatile is conducted 
into condensing chambers where it is collected When the mineral con- 
tains a reasonable amount of cobalt or of gold these metals are extracted 

Uses of Arsenic The metal arsenic has \ery little use in the arts, 
though its compounds find many applications as insecticides, medicines, 
pigments, in tanning, etc The basis of most of these is AsoOs, and 
this is produced directly from the fumes of smelters working on arsenical 
gold, silver and copper ores Only a portion of such fumes are saved, 
however, as even half of those produced at a single smelter center 
(Butte, Montana), would more than supply the entire demand of the 
United States for arsenic and its compounds Under these conditions 
the mining of arsenical pynte as a source of arsenic has ceased so far 
as the United States is concerned 

Lollingite (FeAso) is usually massive, though its rare crystals are 
isomorphous in e\ery respect with those of arsenopynte The pure 
mineral is not common Most specimens are mixtures of lollmgite with 
arsenopynte or other sulphides or arsenides. 

The mineral is silver-white or steel-gray Its streak is grayish black 
Its hardness is 5-5 5 and density about 72 It readily fuses to a mag- 
netic globule, at the same time evolving arsenic fumes It is soluble in 
HN0 3 

It usually occurs in veins associated with other sulphides and arsen- 
ides It is found at Pans, Maine; at Edenville and Monroe, N. Y.; 
at vanous mines in North Carolina, and on Brush Creek, Gunnison 
Co., Colo At the last-named locality the mineral is in star-shaped 
crystalline aggregates, in twins and trillings, associated with siderite 
and barite. 

SYLVANITE GROUP 

The sylvanite group includes at least three distinct minerals, all of 
which are ditellurides of gold or silver. The group is isodunorphous. 
The pure gold tellunde is known only in monochmc crystals, but the 
isomorphous mixtures of the gold and silver compounds occur both in 
monochmc and orthorhombic crystals 



114 DESCRIPTIVE MINERALOGY 

Orthorhombic bipyramidal Monoclmic prismatic 

AuTeo Calavente 

Krennente (Ag Au)Te 2 Syhamte 

All three minerals are utilized as ores of gold While occurring only 
in a few places, they are sufficiently abundant at some to be mined 

Calaverite (AuTe 2 ) 

Calavente is a nearly pure gold chloride However, it is usually 
intermixed with small quantities of the silver tellunde An analysis of a 
specimen from Kalgoorhe, Australia, gave Te=5727, Au=4i 37, 

Ag= 5 8 

Calaverite crystallizes m the monoclmic system (prismatic class) in 
crystals that are elongated parallel to the orthoaxis and deeply striated 
in this direction. Their axial ratio is i 6313 i ' i 1449 with =90 13' 
The prominent forms are ooP 66(100), ooPD(oio), oP(ooi), 
-Poc(ioi), +P6o(ioT), -2Poo(20i), +2P66(2oT), and P(in) 
Twinnmg is common and the resulting tuiins are very complicated 
Usually, however, the mineral occurs massive and granular 

Calavente is opaque, silver-white or bronzy yellow in color and has a 
yellow-gray or greenish gray streak. Its surface is frequently covered 
with a yellow tarnish. The mineral is brittle and without distinct cleav- 
age Its hardness is 2-3 and density 9 04 

On charcoal before the blowpipe the mineral fuses easily to a yellow 
globule of gold, yielding at the same tune the fumes of tellurium oxide. 
It dissolves in concentrated EfeSO.*, producing a deep red solution. When 
treated with HNOs it decomposes, leaving a rusty mass of spongy gold 
The solution treated with HC1 usually yields a slight precipitate of silver 
chloride 

Calaverite is distinguished from most other minerals by the test for 
tellurium It is distinguished from fetzite (p 80), by its crystallization 
and the fact that it gives a yellow globule when roasted on charcoal, 
and from sylvamte by the small amount of silver it contains, its higher 
specific gravity, its color and its lack of cleavage It is distinguished 
from krennente by its crystallization 

Occurrence The mineral occurs in veins with the other tellurides 
associated with gold ores in Calaveras Co , Cal , and at the localities 
mentioned for petzite (see p 81) It is believed to have been deposited 
by pneumatolytic processes or by ascending magmatic water at com- 
paratively low temperatures. 



SULPHIDES, TELLURIDE8, ETC 115 

Uses. The mineral is mined with other tellundes in Boulder Co , 
and at Cripple Creek, Colorado, as an ore of gold 

Sylvamte (Ag Au)Te 2 

Sylvamte is more common than calavente It is an isomorphous 
mixture of gold and silver tellundes in the ratio of about i . i Analyses 
follow 

I Te=62 16 Au=24 45 Ag=i3 39 Total=ioo oo 

II Te=59 78 Au=26 36 Ag = i3 86 " ico oo 

III Te=58 91 Au=29 35 Ag=n 74 k * 100 oo 

I Theoretical for AgTe 2 + \uTe 2 
II and III Specimens trom Boulder Co , Colo 

In crystallization the mineral is isomorphous with calavente, with 
an axial ratio a b . c= i 6339 i : i 1265 and $=90 25' Its crystals 
are usually rich in planes, about 75 ha\mg been identified Their habit 
is usually tabular parallel to ooP ob (GIO), with this plane, P 5c (101), 
oP(ooi), oo P 5b (100) and 2P2(T2i) predominating The mineral also 
occurs in skeleton crystals and in aggregates that are platy or granular 
Twinning is common, \\ith P<X(IOI) the twinning plane Many 
twinned aggregates form networks suggesting writing, hence the name 
" Schnfterz '' often applied to the mineral by the Germans 

Sylvamte is silver-white or steel-gray and has a brilliant metallic 
luster and a silver-white or yellowish gray streak Its hardness is 
between i and 2 and its densiU 7 9-8 3 Moreover, it possesses a per- 
fect cleavage parallel to oo P ob (oio) 

Its chemical properties are the same as those of calavente, but the 
silver precipitate produced by adding HC1 to its solution m HNOs is 
always large It is best distinguished from the gold tellunde by its 
cleavage and from fetzite ((AgAu^Te) and lessite (AgsTe) by its 
crystallization, and by the yellow metallic globule produced when the 
mineral is roasted on charcoal It is distinguishable from krennente by 
its crystallization 

Localities and Origin Sylvanite occurs with the other tellundes in 
veins at Offenbanya and Nagyag in Transylvania, at Cripple Creek and 
m Boulder Co , Colo , near Kalgoorhe, W Australia, in small quan- 
tities near Balmoral in the Black Hills, S D , and at Moss, near Thunder 
Bay, Ontano Like calavente it TV as deposited by magmatic water, or 
by hot vapors 

Uses It is mined with calaverite as a gold and silver ore at Cripple 
Creek and in Boulder Co , Colo. 



CHAPTER V 
THE SULPHO-SALTS AND SULPHO-FERRITES 

THE sulpho-salts are salts of acids analogous to arsenic acid, 
and arsenious acid, HsAsOs, and the corresponding antimony acids 
HsSb04 and EfeSbOs The sulpho-acids differ from the arsenic and the 
antimony acids in containing sulphur in place of oxygen, thus HsAsS-i, 
HsAsSa, H 3 SbS4 and H 3 SbS 3 . The mineral enargite may be regarded as 
a salt of sulpharsenic acid, thus CusAsS-i, copper having replaced the 
hydrogen of the acid Proustite, on the other hand, is AgsAsSs, or a 
salt of sulpharsemous acid. The salts of sulpharsenic acid are called 
sulpharsenates, while those derived from sulpharsemous acid are known 
as sulpharsemtes The sulpharsenates are not represented among the 
commoner minerals, although the copper salt enargite is abundant at a 
few places A number of salts of other sulphur-arsenic acids are known 
but they are comparatively rare 

There is another class of compounds with compositions analogous 
to those of the sulpho-salts, though their chemical nature is not well 
understood This is the group of the sulpho-ferntes We know that 
certain hydro-sides of iron may act as acids under certain conditions 
The sulpho-ferrites may be looked upon as salts of these acids in which, 
however, the oxygen has been replaced by sulphur, as in the case of the 
sulpho-acids referred to above Thus by replacement of by S, m 
feme hydroxide Fe(OH)s the compound Fe(SH)s or HsFeSs results 
The salts of this acid are sulpho-ferrites This acid, by loss of HaS, 
may give rise to other acids in the same way that sulphuric acid (EfeSO/O, 
by loss of HaO, gives nse to pyrosulphuric acid In the case of the 
sulpho-acid we may have HsFeSs H2S=HFeS2 The copper salt of 
this acid is the common mineral chalcopyrite, CuFeS2 

The sulpho-salts are very numerous, but only a few of them are of 
sufficient importance to warrant a description in this book 



116 



SULPHO-SALTB AND SULPHO-FERRITES 117 



THE SULPHARSENITES AND SULPHANTIMONITES 

The sulpharsemtes and sulphantimomtes are denvatives of the 
ortho acids HsAsSs and 



ORTHO SULPHO-SALTS 

The ortho salts are compounds in \\hich the hydrogen of the ortho 
acids is replaced by metals They include a large number of minerals, 
of which the following are the most important. 



Boitrnomte (Cus Pb)s (SbSs)2 Orthorhombic 

Pyrargynte AgsSbSa Hexagonal 

Proustite AgsAsSs Hexagonal 

PYRARGYRITE GROUP 
Pyrargynte (AgsSbSs) 

Pyrargyrite, or dark ruby silver, is an important silver ore, especially 
in Mexico, Chile and the \\estern United States. The name ruby silver 
is given to it because thin splinters transmit deep red light The mineral 
is usually mixed with other ores in compact masses, but it also forms 
handsome crystals 

The composition of pyrargyrite is represented by the formula AggSbSs 
which demands 17 82 per cent S , 22 21 per cent Sb , 59 97 per cent Ag 
Many specimens contain also a small quantity of arsenic, through the 
admixture of the isomorphous compound proustite The analyses given 
below show the effect of the intermixture of the two molecules 

S Sb As Ag Total 

Andreasberg, Harz 17 65 22 36 59 73 99 77 

Zacatecas, Mexico 17 74 22 39 27 60 04 100 44 

Freiberg, Saxony 17 95 18 58 2 62 60 63 99 78 

The crystals of pyrargyrite are rhombohedral and hemunorphic 
(ditngonal pyramidal class), with an axial ratio i : 8038 They are 
usually quite complex and are often twinned. The species is very rich 
in forms, not less than 150 having been reported The most prominent 
of these are ooP2(ii2o), ooP(ioTo), R(ioli), -iR(oil2) and the 
scalenohedrons R 3 (2i3i) and iR 3 (2i34) (Fig ^49) In the commonest 
twinning law the twinning plane is ooP2(ii2o) and the composition 



118 DESCRIPTIVE MINERALOGY 

face oPfooi) The c axes in the twinned portions are parallel and the 
o=P2(ii2~o) planes coincident, so that the t\\m at a hasty glance looks 
like a simple crystal The angle roll /\lioi = 71 22' 

The cleavage of pyrargynte is distinct parallel to R(ioTi) Its frac- 
ture is conchoidal or une\ en The mineral is apparently opaque and its 
color is grayish black in reflected light, but is trans- 
parent or translucent and deep red in transmitted 
light Its streak is purplish red For lithium 
light 03=3084, =2881 It is not an electrical 
conductor 

In the closed tube the mineral fuses easily and 



/ 



ghes a reddish sublimate When heated 



^ sodium carbonate on charcoal it is reduced to a 

P\ra^g\nte * with g^bule of silver, \vhich, when dissolved in nitric 

1 1 20 (a) acid, yields a silver chloride precipitate when 

I treated \\ith a soluble chloride The mineral dis- 



solves in nitric acid with the separation of sulphur 
and a white precipitate of antimony oxide It is also soluble in a 
strong solution of KOH From this solution HC1 precipitates orange 
Sb2Ss (compare proustite) 

The color and streak of p>rargynte, together with its translucency, 
distinguish it from nearly all other minerals Its reaction for silver 
serves to distinguish it from cuprite, dnnalar and realgar, which it some- 
times resembles The distinction between this mineral and its iso- 
morph, proustite, is based on the streak and the reaction for anti- 
mony. 

Pyrargynte occurs as a pseudomorph after native silver. On the 
other hand it is occasionally altered to pynte or argentite, and some- 
times to silver 

Syntheses Microscopic crystals ha\e been made by heating in a 
porcelain tube, metallic silver and antimony chlorides in a current of 
IfeS, and by the action of the same gas at a red heat on a mixture of 
metallic silver and melted antimony* o\ide 

Occurrence, Localities and Origin Pyrargynte occurs in veins asso- 
ciated with other compounds of silver and scmetimes with galena and 
arsenic It is most common in the zone of secondary enrichment of 
silver veins. The crystallized variety is found at Andreasberg in the 
Harz, at Freiberg, in Saxony, at Pnbram, in Bohemia, at many places 
in Hungary, and at Chanarcillo, in Chile The massive variety is worked 
as an ore of silver at Guanajuato in Mexico and in several of the western 
states, as, for instance in the Ruby district, Gunmson Co , and in other 



SULPHO-SALTS AND SULPHO-FERRITES 119 

mining districts m Colorado, near Washoe and Austin, Nevada, and at 
several points in Idaho, Ne\v Mexico, Utah and Arizona 

Uses The mineral is an important ore of silver in Mexico and in 
the western United States It is usually associated with other sulphur- 
bearing ores of sil\er, the metal being extracted from the mixture by 
the processes referred to under argentite, 

Proustite (AgsAsSs) 

Proustite, or light ruby siher, is isomorphous with p\rargynte It 
differs from the latter mineral in containing arsenic m place of antimony 
It occurs both massive and in crystals, and like pyrargynte is an ore of 
silver 

The formula abo\e given demands 19 43 per cent S, 15 17 per cent 
As, and 65 40 per cent sih er The analysis of a specimen from Mexico 
yields figures that correspond \ery nearly to these Cr}stals from 
Chanarcillo contain a slight admixture of the antimony compound 

S As Sb Ag Total 

Mexico 19 52 14 98 65 39 99 89 

Chanarcillo, Chile 19 64 13 85 i 41 65 06 99 96 

Like pyrargynte, proustite is rhombohedral Its crystals are pris- 
matic or acute rhombohedral The forms present on them are much 
less numerous than those on the corresponding 
antimony compound, the predominant ones being 
ocp 2 (ii2o), iR(ioT 4 ), -iR(oil2), R d (2i3i), 
~|R 4 (3557J and other scalenohedrons (see Fig 
50) Twins are common, the t winning planes 
being (i), parallel to JR(iol4) and (2) parallel to 
R(ioTi) The angle io7i Alici = 7i 12'. FlG So-Crystal of 

The cleavage, fracture and haidness of prous- JJJHJ ^ * Jj 
tite are the same as for pyrargynte Its hard- (j/) and -|R, 0112 (). 
ness is 2 and its density is about 5.6 The mineral 
is transparent or translucent Its color is grayish black by reflected 
light and scarlet m transparent pieces by transmitted light. Under the 
long-continued influence of daylight the color deepens until it becomes 
darker than that of pyrargynte Its streak is cirnabar-red to brownish 
black Its luster is adamantine. It is a nonconductor of electncity 
For sodium light 03=3 0877, = 2 7924 

In the closed tube proustite fuses easily and gives a slight sublimate 



120 DESCRIPTIVE MINERALOGY 

of \\hite arsenic oxide In its other chemical properties it resembles 
pyrargyrite except that it gi\es reactions for arsenic \\here this mineral 
reacts for antimony, and yields onh sulphur \\hen dissohed in HNOa 
From its solution in KOH a yellow precipitate of As^Ss is thrown do\\n 
upon the addition of HC1 (compare pyrargyrite) 

Proustite differs from pyra g \nte in Us color, transparency and 
streak, as \vell as in its arsenic reactions It is distinguished from 
cinnabar and cuprite (CuO) b> the arsenic test 

Syntheses Crystals of proustite ha\e been produced by reactions 
analogous to those that yield p\rargynte, when arsenic compounds are 
employed in place of antimon\ compounds 

Occurrence The mineral occurs under the same conditions and with 
the same associates as pyrargyrite and it yields the same alteration 
products as pyrargynte 

Localities and Uses Handsome crystals of proustite occur at 
Freiberg and other places in Saxony, at Wolfach in Baden, at Markirchen 
in Alsace and at Chanarcillo in Chile It is associated with pyrargyrite 
and with other ores of silver 

In the western United States it is quite abundant, more particular!} 
in the Ruby district, Colorado, at Poorman lode in Idaho, and in all other 
localities where pyrargynte occurs In many it is mined as an ore of 
silver 

Bournonite ((Pb Cu 2 )3(SbS 3 ) 2 ) 

Bournomte is a comparatively rare mineral It occurs either in 
compact or granular masses or in well developed crystals of a steel 
gray color It is not of any economic importance except as it may be 
mixed with other copper compounds exploited for copper 

Analyses of bournomte from two localities are given below 

S Sb 

I- 19 3 6 2 3 57 
n. 19 78 23 80 

I Liskeard, Cornwall, England 
II Felsobinya, Hungary 

These analyses are by no means accurate, but they show the compo- 
sition of the mineral to be approximately Pb, Cu, Sb and S, in which the 
elements are combined in the following proportions 8=19 8 per cent, 
Sb=24 7 per cent, Pb 42 5 per cent, Cu 13 per cent 

Bournonite crystals are orthorhombic (rhombic bipyramidal class), 



As 


Pb 


Cu 


Fe 


Total 


47 


4i 95 


13 27 


68 


99 30 


- 


42 07 


12 82 


20 


98 67 



SULPHO-SALTS AXD 3ULPHOFERRITES 



121 



with a . b c= 9380 i 8969 They are usually tabular 'Fig 51;, or 
short, prismatic in habit, and are often in repeated twins fFig 52*, with 
wheel-shaped or cross-like forms The principal planes observed on 
them are oP(ooi),P<^(ioij, POD (011 ),iP(ii2), wP(noi, xPxiioo, 
and oo P oc (oio), though 90 or more planes are kno\\ n The most com- 
mon twinning plane is oo P(no) Angle IIOAIIO 86 20' 

The luster of the mineral is brilliant metallic Its cclcr and streak 
are steel-gray Its cleavage is imperfect, parallel to QC P c f oio ; and its 
fracture conchoidal or uneven Its hardness is 2 5-3 and density 5 8 
Like most other metallic minerals it is opaque It is a \ ery poor con- 
ductor of electricity 

In the closed tube bournomte decrepitates and yields a dark red sub- 
limate In the open tube, and on charcoal, it gives reactions for Sb, S, 
Pb and Cu When treated with nitric acid it decomposes, producing a 





FIG 51 FIG s- 

FIG 51 Bournomte Crystal \uth oP ooi (c], P 55 , 101 (0), \P 112 f u) and P x, 

on in) 

FIG 52 Bournonite Fourlmg Tuinned about x P, no (m) Form c same as in 
Fig 51 b = =c P oo (oio; and a *= oc P 55 s 100) 

blue solution of copper nitrate that turns to an intense azure blue when 
an excess of ammonia is added In this solution is a residue of sulphur 
and a white precipitate that contains lead and antimon\ . 

Bournomte is distinguished from most other minerals by its reactions 
for both antimony and sulphur. From other sulphantunonites it is 
distinguished by its color, hardness and density. 

On long exposure to the atmosphere bournomte alters to the car- 
bonates of lead (cerussitej and copper (malachite and azunte) 

Synthesis Crystals of bournomte have been obtained by the action 
of gaseous HkS on the chlorides and oxides of Pb, Cu and Sb, at moderate 
temperatures 

Occurrence The mineral occurs principally in veins with galena, 
sphalerite, stibmte, chalcopynte and tetrahednte 

Localities. Good crystals are found in the mines at Neudorf, Harz; 
at Pnbram, m Bohemia, at Felsobanya, Kapnik and other places 
in Hungary, and at various places in Chile. In North America it has 



122 DESCRIPTIVE MINERALOGY 

been found at the Boggs Mine in Yavapai Co , Ariz , in Montgomery 
Co , Ark , and at Marmora, Hastings Co , and Darling, Lanark Co , 
Ontario. 

THE SULPHDIARSENITES AND SULPHDIANTIMONITES 

A large number of sulpho-salts are apparent!} salts of acids that 
contain two or more atoms of As or Sb in the molecule These acids 
may be regarded as derived from the ortho aads by the abstraction of 
HsS, thus The arsemous acid containing two atoms of As may be 
thought of as 2H3AsS3-H 2 S=H4As 2 S5 Acids with larger proportions 
of arsenic may be regarded as derived in a similar manner from three or 
more molecules of the ortho acid Only a few of these salts are common 
as minerals. Among the more common are two that are lead salts of 
derivatives of sulpharsemous and sulphantimonous acids, 

Jamesomte (PbsSbgSs) and Dufrenoysite (Pb2AsgS5) 

Jamesonite and dufrenoysite are lead salts of the acids H4Sb2Ss and 
H4As2Ss Both minerals occur in acicular and columnar orthorhombic 
crystals and in fibrous and compact masses of lead-gray color Their 
cleavage is parallel to the base The minerals are brittle and have an 
uneven to conchoidal fracture Their hardness is 2-3 and density 
5 5-6 The streak of jamesomte is grayish black, and of dufreynosite 
reddish brown. Both minerals are easily fusible They are soluble in 
HC1 with the evolution of EfeS, giving a solution from which acicular 
crystals of PbCfe separate on cooling They are decomposed by HNOs, 
with the separation of a white basic lead salt They are found in veins 
with antimony and sulphide ores abroad and at several points in Nevada 
and in the antimony mines in Sevier Co , Arkansas 



THE SDLPHARSEWATES AND SDLPHANTIMOITATES 



The sulpharsenates are salts of sulpharsenic acid, HaAsS^ and the 
sulphantimonates, the salts of the corresponding antimony acid, HsSbS^ 
These compounds are much less numerous among the minerals than the 
sulpharsenites and sulphantimomtes. Moreover, no member of the 
former groups is as common as several of the members of the latter 
The most important member is the mineral enargite (CusAsS^ an ortho- 
sulpharsenate, which in a few places is wrought as a copper ore. 



SULPHO-SALTS AND SULPHO-FERRITES 123 



Enargite 

Enargite, though a rare mineral, is so abundant at a few points that 
it has been mined as an ore of copper 

Theoretically, the mineral is 8=326, As=i9i, 01=483 Most 
specimens, however, contain an admixture of the isomorphous anti- 
mony compound, jamaiimte^ and consequently sho\v the presence of 
antimony. A specimen from the Rarus Mine, Butte, Montana, yielded 

S As Sb Cu Fe Zn Ins Total 

31 44 17 91 i 76 48 67 .33 10 ii 100 32 

The mineral crystallizes in the orthorhombic system (bipyramidal 
class), m crystals with an axial ratio 8694 : i : 8308 Their habit is 
usually prismatic, and they are strongly striated 
vertically. The crystals are usually highly modi- 
fied, with the following forms predominating 
oo P 06(100), ooP(no), ooP3(i2o), ooP^f^o), 
oo P 06 (oio), and oP(ooi) (Fig 53) Stellar trill- 
ings, with ooP2(i2o) the twinning plane, have a 
pseudohexagonal habit. The mineral occurs also 



in columnar and platy masses FIG ^ _ Enarglte Crys _ 

Enargite possesses a perfect prismatic cleavage tal wth M Pj 1IO (m ^ 
and an uneven fracture. It is opaque with a OOP 55,100 (a), >pr, 
grayish black color and streak. Its hardness is 3 i2o(A)andoP,oor(c). 
and density 44. It is a poor electrical conductor. 

It is easily fusible before the blowpipe When roasted on charcoal 
it gives the reactions for S and As, and the roasted residue when 
moistened with HC1 imparts to the flame the azure-blue color char- 
acteristic of copper. In the closed tube it decrepitates and gives a 
sublimate of S. When heated to fusion it yields a sublimate of arsenic 
sulphide The mineral is soluble in aqua regia 

Enargite is easily recognized by its crystallization and blowpipe 
reactions 

Occuiience. Enargite is associated with other copper ores in veins 
filled by magmatiC water at intermediate depths and in a few replace- 
ment deposits 

Localities Although not widely distributed, enargite occurs in large 
quantities in the copper mines near Morococha, Peru; Copiap6, Chile; 
in the province of La Rioja, Argentine; on Luzon, Philippine Islands, 



124 DESCRIPTIVE MINERALOGY 

and in the United States, at Butte, Montana in the San Juan Moun- 
tains, Colorado and m the Tmtic District, Utah 

Uses It is smelted as an ore of copper At the Butte smelter it 
furnishes the arsenic that is separated from the smelter fumes and placed 
upon the market as arsenic oxide (see p 113) 

THE BASIC SULPHO-SALTS 

The basic sulpho-salts are compounds in \\hich there is a greater 
percentage of the basic elements (metals, etc), present than is 
necessary to replace all the hydrogen of the ortho acids Thus, the 
copper orthosulpharsenate, enargite, is CusAsSU The mineral steph- 
anite is AgsSbS* and the pure silver polybasite AggSbSe 

Since three atoms of Ag are sufficient to replace all the hydrogen 
atoms m the normal acid containing one atom of antimony and the 
quantities of silver present in stephamte and polybasite are in excess 
of this requirement, the two minerals are described as basic The 
exact relations of the atoms to one another in the molecules are 
not known 

Although the number of basic sulpho-salts occurring as minerals is 
large only four are common These are: 

Stephamte AgoSbS* Orthorhombic 

Polybasite (Ag - Cu^SbSc Monoclimc 

Tetrahednte (R")4Sb 2 S7 Isometric 

T&nnantite (R'^AsoS? Isometric 

Stephanite (Ag 5 SbS 4 ) 

Stephanite, though a comparatively rare mineral, is an important ore 
of silver in some camps It occurs massive, in disseminated grains and 
as aggregates of small crystals Analyses indicate a composition very 
dose to the requirements of the formula AgsSbS4 

S Sb Ag AsandCu Total 

Theoretical . . . 16 28 15 22 68 50 100 oo 

Crystals, Chanarollo, Chile 16 02 15 22 68 65 tr 99 89 

Stephanite crystallizes in hemimorphic orthorhombic crystals (rhom- 
bic pyramidal class), with an axial ratio .6291 : i : .6851. The crystals 
are highly modified, 125 forms having been identified upon them. They 
have usually the habit of hexagonal prisms, their predominant planes 




SULPHO-SALTS AND SULPHO-FERRITES 125 

being ooP(no) and oop 06(010), terminated by oP(ooi), P(in) and 
2Poc (021) at one or the other end of the c aus (Fig 54) Twins are 
common, with oo P(no) and oP(ooi) the t\\ inning planes 

The mineral is black and opaque and its streak is black Its hard- 
ness is 2 and density =6 2 63 It cleaves 
parallel to oo P 06 (oio) has an uneven frac- 
ture, and is a poor conductor of electricity 

On charcoal stephamte fuses \ery easily 
to a dark gray globule, at the same time 
yielding the \vhite fumes of antimony oxide FIG. 54 Stephanite Crystal 
and the pungent odor of S0 2 Under the *th oP, oox (), <*?, 
reducing flame the globule is reduced to oio(ft) ooP, !io W, |P, 

,, , m-, i T t - S3 2 (P)> " 21 W- 

metallic silver. The mineral dissolves in 

dilute nitric acid and this solution gives a white precipitate with HC1. 

Stephamte is easily distinguished from other black minerals by its 
easy fusibility, its crystallization, and its reactions for Ag, Sb and S 

Localities The mineral is associated Tvith other silver ores in the 
zone of secondary enrichment of veins at Freiberg, Saxony, Joachimsthal 
and Pribram, Bohemia, the Comstock Lode and other mines in the 
Rocky Mountain region and at many points in Mexico and Peru. 

Uses It is mined together with other compounds as an ore of silver 
It is particularly abundant in the ores of the Comstock Lode, Nev., and 
of the Las Chispas Mine, Sonora, Mex. 

Polybasite ((Ag-Cu) 9 SbS 6 ) 

Polybasite is the name usually applied to the mixture of basic sulph- 
ai^fomtes and sulpharsemtes of the general formula R^Sb-AsJSe, in 
which R'= Ag and Cu. More properly the name is applied to the anti- 
monite, and the corresponding arsenite is designated as pearceite. Sev- 
eral typical analyses follow 

S As Sb Ag Cu Fe Pb Ins Total 

I 17 46 7 56 . . 59 22 15 65 - 99 89 

H- 17 7i 7 39 SS-I7 *S ii i 05 42 99 85 

HI. 15 43 5 10.64 68 39 $ 13 . . 100 09 

IV. 16 37 3 88 5 is 6793 607 . .76 ... 100.18 

I Pearceite Veta Rica Mine, Sierra Mojada, Mexico 
II. Crystals of pearceite, Drumlummon Mine, Marysville, Montana. 

III. Polybasite, Santa Lucia Mine, Guanajuato, Mexico 

IV. Polybasite, Quespisiza, Clule 



126 DESCRIPTIVE MIXERALOGY 

The crystallization of the two minerals, which are completely isomor- 
phous, is monoclinic (prismatic class) Their axial ratios are 



Pearceite, a : b : c= 1.7309 : i : i 6199 =9 9' 
Polybasite, =i 7309 : i : i 5796 =90' 



Y 

o 



The crystals are commonly tabular or prismatic, with a distinct 
hexagonal habit. The prominent forms are oP(ooi), P(ni) and 
2P 55 (20!). Contact twinning is common, with oo P(no) the twinning 
plane, and oP(ooT) the composition plane 

Both minerals are nearly opaque Except in very thin splinters 
they are steel-gray to iron-black in color Very thin plates are trans- 
lucsnt and cherry-red Their streaks are black Their cleavage is 
perfect parallel to oP(ooi) and their fracture uneven Their hardness 
is 2-3, and density 6-6 2 

Both minerals are easily fusible They usually exhibit the reactions 
for Ag, Sb, As and S 

They are readily distinguished from all other minerals but silver 
sulpho-salts by their blowpipe reactions From these they are distin- 
guished by their crystallization Pearceite and polybasite are distin- 
guished from one another by the relative quantities of As and Sb they 
contain 

Occurrence Both minerals occur in the zone of secondary enrich- 
ment in veins of silver sulphides. 

Localities Polybasite was an important ore of silver in the Comstock 
Lode, Nevada It is at present mined with other silver ores at Ouray, 
Colorado, at Marysville, Montana, at Guanajuato, Mexico, and at 
various points in Chile Good crystals occur at Freiberg, Saxony, at 
Joachimsthal, Bohemia, and in the mines in Colorado, Mexico and Chile. 

TETRAHEDRITE GROUP 

The name tetrahedrite is given to a mixture of basic sulphanti- 
monites and sulpharsenites crystallizing together in isometric forms with 
a distinct tetrahedral habit (hextetrahedral dass) The isomorphism 
is so complete that all gradations between the various members of the 
group are frequently met with The arsenic-bearing member of the 
series is known as tennantite and the corresponding antimony member as 
letrakednte The latter is the more common 

The following six analyses of tetrahedrite will give some idea of the 
great range in composition observed in the species. 



SULPHO-SALTS AND St'LPHO-FERRITES 127 

S Sb As Cu Fe Zn Ag Hg Pb Total 

I 27 60 25 87 tr 35 85 2 66 5 15 2 30 99 43 

II 23 51 17 21 7 67 42 oo 8 28 49 55 99 71 

III. 24 44 27 60 27 41 4 27 2 31 14 54 . 100 57 

IV 24 89 30 18 tr 32 80 5 85 07 5 57 99 36 

V 21 67 24 72 33 53 56 i So 16 23 98 51 

I Xewbur>port, Mass 

II Cajabamba, Peru 

HI Star City, Xev 

IV Poracs, Hungary. 

V Arizona. 

Upon examination these are found to correspond approximately to 
the formula R' ^SbaS:, in which the R" is Cu 2 , Pb, Fe, Zn, Hg, Ag 2 and 
sometimes Co and Ni When R is replaced entirely by copper, the 
formula (CusSb2S-) demands 23 i per cent S, 24 8 per cent Sb and 52 i 
per cent Cu 

Analyses of tennantite yield analogous results that may be repre- 
sented by the formula CusAs2Sr which demands 26 6 per cent S, 20 76 
per cent As and 52 64 per cent Cu 

Analyses of even the best crystallized specimens rarely yield As or 
Sb alone. Moreover, nearly all show the presence of Zn in notable 
quantity The great variation noted in the composition of different 
specimens which appear to be pure crystals has led to the proposal of 
other formulas than those given abo\e some being simpler and others 
more complex It is possible that the variation may be explained as 
due, in part, to some kind of solid solution, rather than as the result 
solely of isomorph'jus replacement It is more probable, however, that 
it is due to the intergrowth of notable quantities of various sulphides 
with the sulpho-salts 

There is still considerable confusion in the proper naming of the mem- 
bers of the series, but generally the forms composed predominantly of 
Cu, Sb and S with or without Zn are known as tetrahednte and those 
containing As m place of Sb as tennantite, although several authors 
confine the use of the latter term to arsenical tetrahedrites containing a 
notable quantity of iron 

Since the members of the tetrahedrite series often contain a large 
quantity of metals other than Cu and Zn the group has been so sub- 
divided as to indicate this fact Thus, there are argentiferous, mercurial 
and plumbiferous varieties of tetrahedrite Some of these varieties are 
utilized as ores of the metals that replace the copper and zinc in the more 



128 DESCRIPTIVE MINERALOGY 

common varieties The relations of the ordinary (II) and the bis- 
muthiferous tennantites (III) to tetrahednte (I) are shown by the fol- 
lowing three analyses. 

S As Sb Bi Cu Fe Ag Pb Co Total 

I 24 48 tr 28 85 45 39 i 3* " IQ o 15 

II 26 61 19 03 51 62 i 95 99 21 

III 29 10 ii 44 2 19 13 07 37 52 6 51 04 i 20 101 07 

I Fresney d'Oisans, France. 
II Cornwall, England. 
Ill Cremenz, Switzerland 

The crystals of both tetrahedrite and tennantite are tetrahedral in 
habit, the principal forms on them consisting of the simple tetrahedron 

and complex tetrahedrons such as (211), (332) together with 

the dodecahedron, ooQ(iio) and the cube, ooOoo(ioo) (Fig. 55) 
Twins are common with 0(in) the twinning 
plane. These are sometimes contact twins 
and sometimes interpenetration twins. Some 
crystals are very complicated, because of the 
presence on them of a great number of forms 
The total number of distinct forms that have 
been identified is about 90. The mineral 

m L j ^ occurs also in granular, dense and earthy 
FIG 55 Tetrahednte Crys- 6 ' J 

o masses. 

tal with -, 1 1 1 W , " o, The fracture of the tetrahedrites is uneven 

no (d) and fO, 332 (). Their hardness varies between 3 and 4 5 and 

their density between 4 4 and 5 i Their color 

is between dark gray and iron-black, except in thin splinters, which 
sometimes exhibit a cherry-red translucency. Their streak is like their 
color. All tetrahedrites are thermo-electric. 

The chemical properties of the different varieties of tetrahedntes 
vary with the constituents present. All give tests for sulphur and for 
either antimony or arsenic, and all show the presence of copper in a 
borax bead. The reactions of other metals that may be present may 
be learned by consulting pages 483-494. 

The crystals of tetrahedrite are so characteristic that there is little 
danger of confusing the crystallized mineral with other minerals of the 
same color. The massive forms resemble most dearly arseno$yrite y 
lownmtie and chalcocite From these the tetrahedrites are 




SULPHO-SALTS AND SULPHO-FERRITES 129 

best distinguished by their hardness, together with their blowpipe reac- 
tions 

Tetrahednte appears to suffer alteration quite readily, since pseudo- 
morphs of several carbonates and sulphides after tetrahednte crystals 
are well known 

Syntheszs Crystals of the tetrahedrites have been made by passing 
the vapors of the chlorides of the metals and the chlorides of arsenic or 
antimony and EfeS through red-hot porcelain tubes They have also 
been observed in Roman coins that had Iain for a long time in the hot 
springs of Bourbonne-les-Bains, Haute-Marne, France. 

Occurrence The tetrahedrites are very common in the zone of 
secondary enrichment of sulphide veins and in impregnations They 
occur associated with chalcopyrite, pynte, sphalerite, galena and other 
silver, lead and copper ores in nearly all regions where the sulphide ores 
of these metals are found They occur also as primary constituents of 
veins of silver ores, where they were deposited by magmatic waters. 

Localities In the United States tetrahedrite occurs at the Kellogg 
Mines, ten miles north of Little Rock, Arkansas, near Central City and 
at Georgetown, Colorado; in the Ruby and other mining districts in 
the same State; at the De Soto Mine in Humboldt Co , Nevada, and 
at several places in Montana, Utah and Arizona It is found also in 
British Columbia and in Mexico, and at Broken Hill, New South Wales 

The arsenical tetrahedrites are not quite as common as is the anti- 
monial variety Excellent crystals occur in the Cornish Mines, at 
Freiberg in Saxony, at Skutterud in Norway, and at Capelton, 
Quebec 

Uses. The mineral is used to some extent as an ore of silver or of 
copper, the separation of the metals being effected in the same way as 
in the case of the sulphides of these substances. 

THE SULPHO-FERRITES 

Only two sulpho-f emtes are sufficiently important to merit descrip- 
tion here Both of these are copper compounds and both are used as 
ores of this metal, one chalcopyrite being one of the most important 
ores of the metal at present worked 

The first of these minerals discussed, bornite, is a basic salt of 
the acid EfeFeSa, the second is the salt of the derived acid HFeS2, 
which may be regarded as the normal acid from which one molecule of 
H 2 S has been abstracted (see p. n6], 



130 . DESCRIPTIVE MINERALOGY 

Bornite (Cu 5 FeS 4 ) 

Bormte, known also as horseflesh ore because of its peculiar purplish- 
red color, is found usually massive In Montana and in Chile it con- 
stitutes an important ore of copper 

Bornite is probably a basic sulpho-femte, though analyses yield 
lesults that vary quite widely, especially in the case of massive varieties 
This variation is due to the greater or less admixture of copper sulphides, 
mainly chalcocite, with the bormte The theoretical composition of the 
mineral is 25 55 S, 63 27 Cu, and 11.18 Fe The analyses of a crystallized 
variety from Bristol, Conn , and of a massive variety from the Bruce 
Mines, Ontano, follow. 

S Cu Fe Ins Total 

Bristol, Conn . 25 54 63 24 n 20 99 98 

Bruce Mines, Ont 25 39 62 78 n 28 30 99 75 

The crystallization of bormte is isometric (hexoctahedral class), in 
combinations of oo O oo (ico), oo 0(iio),0(rn), and sometimes 202(211) 
Crystals often form mterpenetration twins, with the twinning plane 

The fracture of the mineral is conchoidal, its hardness 3 and density 
about 5 On fresh fracture the color varies from a copper-red to a pur- 
plish brown Upon exposure alteration rapidly takes place covering 
the mineral with an iridescent purple tarnish. Its streak is grayish 
black It is a good conductor of electricity 

Chemically, the mineral possesses no characteristics other than those 
to be expected from a compound of iron, copper and sulphur It dis- 
solves in nitric acid with the separation of sulphur 

It is easily recognized by its purplish brown color on fresh fractures 
and its purple tarnish. 

Bornite alters to chalcopyrite, chalcocite. covellite, cuprite (CuaO), 
chrysocolla (CuSiQs 2H20) and the carbonates, malachite and azurite. 
On the other hand, bornite pseudomorphs after chalcopyrite and chal- 
cocite are not uncommon 

Syntheses Roman copper coins found immersed in the water of 
warm springs in France have been partly changed to bornite. Crystals 
have been formed by the action of EkS at a comparatively low tempera- 
ture (ioo-2oo C ), upon a mixture of CuaO, CuO and Fe20s 

Occurrence and Origin Bornite is usually associated with other 
copper ores in veins and lodes, where it is in some cases a primary min- 
eral deposited by magmatic waters and in others a secondary mineral 
produced in the zone of enrichment of sulphide veins. It also sometimes 



SULPHO-SALTS AND SULPHO-FERRITES 131 

impregnates sedimentary rocks, where its origin is part due to contact 
action. 

Localities The crystallized mineral occurs near Redruth, Cornwall 
Eng , and at Bristol, Conn The massive mineral is found at many 
places in Norway and Sweden It is the principal ore of some of the 
Bolivian, Chilian, Peruvian and Mexican mines and of the Canadian 
mines near Quebec In the United States it has been mined at 
Bristol, Conn , and at Butte, Montana 

Uses Bornite is mined with chalcopyrite and other copper com- 
pounds as an ore of this metal 

Chalcopynte (CuFeS2) 

From an economic point of \ie\\ this mineral is the most important 
of the sulpho-salts, as it is one of the most important ores of copper 




FIG 56 FIG 57 FIG 58 

FIG. 56 Chalcopynte Crystal with P, in (p), -P, ill (p) and 2? x> , 201 (3). 

IP Pz 

FEG 57 Chalcopynte Crystal with , 772 (&J and , 212 (x) The form ^ 

2 2 

sometimes approaches P(zio) and x approaches P *s (xoi 1 ) 
FIG 58 Chalcopynte Twinned about P(iu) 

known. It occurs both massive and crystallized. From its similarity 
to pyrite in appearance it is often known as copper pyrites. 

Crystallized specimens of chalcopyrite contain 35 per cent S, 34 5 
per cent Cu and 30.5 per cent Fe, corresponding to the formula CuFeSk, 
i e , a copper salt of the acid HFeS2 The mineral often contains small 
quantities of intermixed pyrite. It also contains in some instances 
selenium, thallium, gold and silver 

The crystallization of chalcopynte is in the sphenoidal, hemihedral 
division of the tetragonal system (tetragonal scalenohedron class). 



132 DESCRIPTIVE MINERALOGY 

P 
The crystals are usually sphenoidal in habit with the sphenoids -(in), 

3p 

and (332) the predominant forms (Figs 56 and 57) In addition to 

2 

these there are often present also oo P oo (100), oo P(no), 2? oo (201), 

ff 
and a very acute sphenoid that is approximately (772), supposed to be 

p 

due to the oscillation of oo P(no) and -(in) (Fig 57) Twins are quite 

common, with the twinning plane parallel to P (Fig 58). The plus 
faces of the sphenoid are often rough and striated, while the minus faces 
are smooth and even. 

The fracture of the mineral is uneven. Its hardness is 3 5-4 and 
density about 4.2. Its luster is metallic and color brass-yellow Old 
fracture surfaces are often tarnished with an iridescent coating Its 
streak is greenish black. It is an excellent conductor of electricity 

On charcoal the mineral melts to a magnetic globule. When mixed 
with Na2COs and fused on charcoal, a copper globule containing iron 
results. When treated with nitric aad it dissolves, forming a green 
solution in which float spongy masses of sulphur The addition of 
ammonia to the solution changes it to a deep blue color and at the same 
time causes a precipitate of red feme hydroxide. 

From the few brassy colored minerals that resemble it, chalcopyrite 
is distinguished by its hardness and streak. 

When subjected to the action of the atmosphere or to percolating 
atmospheric water chalcopyrite loses its iron component and changes 
to covelhte and chalcocite The iron passes into limomte. Bornite, 
copper and pyrite are also frequent products of its alteration. In the 
oxidation zone of veins it yields limonite, the carbonates, malachite and 
azurite, and cuprite (Cu20). When exposed to the leaching action of 
water, limonite alone may remain to mark the outcrop of veins, the 
copper being carried downward in solution to enrich the lower portions 
of the vein. The deposit of limonite on the surface is known as 



Syntheses Crystals of chalcopyrite have been produced by the 
action of HaS upon a moderately heated mixture of CuO and F^Os 
cndosed in a glass tube. The mineral has also been made by the action 
of warm spring waters upon ancient copper coins. It is also a fairly 
common product of roasting-oven operations 

Occurrence and Origin. Chalcopyrite is widely disseminated as a 
primary vein mineral, and is often found in nests in crystalline rocks. 



SULPHO-SALTS AND SULPHO-FERRITES 133 

It also impregnates slates and other sedimentary rocks, schists and 
altered igneous rocks where, in some cases, it is a contact deposit 
and in others is original It is also formed by secondary processes caus- 
ing enrichment of copper sulphide veins Its most common associ- 
ates are galena, sphalerite and pyrite. It is the principal copper ore 
m the Cornwall mines, where it is associated with cassitente (Sn02), 
galena and other sulphides. It is also the important copper ore of 
the deposits of Falun, Sweden, of Namaqualand in South Africa, 
those near Copiapo in Chile, those of Mansfeld, Germany, of the Rio 
Tinto district in Spain, of Butte and other places in Montana, and of 
the great copper-producing districts in Arizona, Utah and Nevada. 

Crystals occur near Rossie, Wurtzboro and Edenville, N. Y., at the 
French Creek Mines, Chester Co., Penn., near Finksburg, Md., and at 
many other places 

Extraction The mineral is concentrated by mechanical methods. 
The concentrates are roasted at a moderately high temperature, the iron 
being transformed into oxides and the copper partly into oxide and 
partly into sulphide. Upon further heating with a flux the iron oxide 
unites with this to form a slag and the copper sulphide melts, and collects 
at the bottom of the furnace as " matte/' which consists of mixed copper 
and copper sulphide. This is roasted in a current of air to free it from 
sulphur. By this process all of the copper is transformed into the oxide, 
which may be converted into the metal by reduction. The metal is 
finally refined by electrical processes. Much of the copper obtained 
from chalcopyrite contains silver or gold, or both, which may be recov- 
ered by any one of several processes. 

Uses. A large portion of the copper produced in the world is obtained 
by the smelting of chalcopyrite and the ores associated with it. 

Production. The world's total product of copper has been referred 
to in another place (p. 55). Of this total (2,251,300,000 Ib.) the United 
States supplied, in 1912, 1,243,300,000 Ib., of which about 1,000,000,000 
Ib. were obtained from sulphide ores. Arizona and Montana produced 
the greater portion of this large quantity, the former contributing about 
359,000,000 Ib. to the aggregate, and the latter 308,800,000 Ib Out- 
side of the United States the most important copper-producing countries 
are Mexico, Japan, Spain and Portugal, Australia, Chile, Canada, 
Russia, Peru and Germany, in the order named. Practically all of this 
copper, except that from Japan and Mexico, is extracted from sulphide 
ores. 



CHAPTER VI 

THE CHLORIDES BROMIDES IODIDES \ND FLUORIDES 

THE salts belonging to this group are 'compounds of metals with 
hydrochloric (HC1), h>drobromic (HBr), hydnodic (HI) and hydro- 
fluoric (HF) acids Only a few are of importance Of these some are 
simple chlorides, others are simple fluorides, others are double chlorides 
or fluorides (i e cryolite, AlFa^NaF), and others are double hydrox- 
ides and chlorides (atacamite) 

THE CHLORIDES 

The simple chlorides crystallize in the isometric system, but in differ- 
ent classes in this system. They comprise salts of the alkalies, K, Na 
and NKi, and of silver Of these only three mmerals are of importance, 
viz.: sylmte, hahte and cerargynte 

Halite (Had) 

Halite, or common salt, is the best known and most abundant of the 
native chlorides It is a colorless, transparent mineral occurring in 
crystals, and in granular and compact masses 

Pure halite consists of 39 4 per cent Cl and 60 6 per cent Na The 
mineral usually contains as impurities clay, sulphates and organic 
substances The several analyses quoted below indicate the nature of 
the commonest impurities and their abundance in typical specimens 

NaCl CaCl MgCl CaS0 4 Na 2 S0 4 Mg 2 S0 4 Clay H 2 

I 97 35 ... i 01 43 23 30 

II. 90 3 . 5 oo 2 oo 2 oo 70 

III, 98 88 tr tr .79 33 

I Stassfurt, Germany. 
II Vic, France 
III. Petit Anse, La. 

The crystallization of halite is isometric (hexoctahedral class), the 
principal forms being ooOoo(ioo), 0(iu) and ooO(no) Often the 

134 




CHLORIDES, FLUORIDES, ETC 135 

faces of the forms are hollowed or depressed giving nse to what are called 
" hopper crystals " (Fig 59). The mineral occurs also in coarse, gran- 
ular aggregates, in lamellar and fibrous masses and in stalactites 

Its cleavage is perfect parallel to oo oo (100) Its fracture is con- 
choidal Its hardness is 2-2 5 and density about 217 Halite, when 
pure, is colorless, but the impurities present often color it red, gray, 
yellow or blue The bright blue motthngs obsened in 
many specimens are thought to be due to the presence 
of colloidal sodium. The mineral is transparent or 
translucent and its luster is \itreous. Its streak is 
colorless Its saline taste is well known. It is 
diathermous and is a nonconductor of electricity. p rG 59 Hcpper- 
The mineral is plastic under pressure and its plasticity Shaped Cube of 
increases with the temperature Its index of refraction Halite 
for sodium light, = i 5442 

In the closed tube halite fuses and often it decrepitates. When 
heated before the blowpipe it fuses (at 776) and colors the flame yellow. 
The chlorine reaction is easily obtained by adding a small particle cf the 
mineral to a microcosmic salt bead that has been saturated with copper 
oxide. This, when heated before the blowpipe, colors the flame a bnl- 
hant blue. The mineral easily dissolves in water, and its solution yields 
an abundant white precipitate with silver nitrate. 

The solubility of halite is accountable for a large number of 
pseudomorphs. The crystals embedded in clays are gradually dissolved, 
leaving a mold that may be filled by other substances, which thus 
become pseudomorphs. 

Syntheses. Crystals of halite have been produced by sublimation 
from the gases of furnaces, and by crystallization from solution contain- 
ing sodium chloride. 

Occurrence and Origin Salt/occurs most abundantly in the water of 
the ocean, of certain salt lakes, of brines buned deep within the rocks in 
some places, and as beds interstratified with sedimentary rocks. In the 
latter case it is associated with sylvite (KC1), anhydrite (CaSO*), gypsum 
(CaSO 4 2H 2 O), etc., which, lite the halite, are believed to have been 
formed by the drying up of salt lakes or of portions of the ocean that 
were cut off from the main IxxLy of water, since the order of occurrence 
of the various beds is the sa me as the order of deposition ot the corre- 
sponding salts when precipitated by the evaporation of sea water at 
varying temperatures (Ojanp pp. 22, 23.) 

Below are given figures* showing the composition of the salts in the 
water of the ocean, of GF -at Salt Lake, and of the Syracuse, N. Y. and 



136 DESCRIPTIVE MINERALOGY 

Michigan artificial brines (produced by forcing water to the buned rock 
salt) 

NaCl CaCk MgCl 2 NaBr KC1 Na 2 S0 4 K 2 S0 4 CaS0 4 MgS0 4 
I 77 07 7 86 i 30 3 89 4 63 5 29 

II. 79 57 10 oo 6 25 3 60 58 

III 95 97 90 69 . 2 54 

IV. 91 95 3 19 2 48 2 39 

I Atlantic Ocean 

II Great Salt Lake 

HI New York bnnes 

IV Michigan bnnes 

Localities The principal mines of halite, or rock salt, are at Wie- 
liczka, Poland, Hall, Tyrol, Stassfuit, Germany, where fine crystals 
are found, the Valley of Cardova, Spain, in Cheshire, England and in 
the Punjab region of India At Petit Anse in Louisiana, in the vicinity 
of Syracuse, N Y , and in the lower peninsula of Michigan thick beds 
of the salt are buried in the rocks far beneath the surface Much of the 
salt is comparatively pure and needs only to be crushed to become usable 
In most cases, however, it is contaminated with clay and other sub- 
stances In these cases it must be dissolved in water and recrystallized 
before it is sufficiently pure for commercial uses 

The best known deposits are at Stassfurt where there is a great thick- 
ness of alternating layers of halite, sylvite (KC1), anhydrite, gypsum, 
kieseiite (MgSQa-IfeO) and various double chlorides and sulphates of 
potassium and magnesium. Although the halite is in far greater quan- 
tity than the other salts, nevertheless, the deposit owes most of its value 
to the latter, especially the potassium salts (comp. pp. 137, 142) 

Uses. Besides its use in curing meat and fish, salt is employed in 
glazing pottery, in enameling, in metallurgical processes, for clearing 
oleomargarine, making butter and in the more familiar household oper- 
ations. It is also the chief source of sodium compounds. 

Production Most of the salt produced in the United States is ob- 
tained directly from rock salt layers by mining or by a process of solu- 
tion, in which water is forced down into the buned deposit and then to 
the surface as bnne, which is later evaporated by solar or by artificial 
heat In the district of Syracuse, N. Y , salt occurs in thick lenses 
interbedded with soft shales In eastern Michigan and in Kansas salt 
is obtained from buried beds of rock salt, and in Louisiana from great 
dome-like plugs covered by sand, day and gravel. Some of the masses 
in this State are 1,756 ft. thick. 



CHLORIDES, FLUORIDES, ETC 137 

The salt production of the United States for 1912 amounted to 33,- 
324,000 barrels of 280 Ib each, valued at $9,402,772 Of this quantity 
7,091,000 barrels were rock salt 

The imports of all grades of salt during the same time were about 
1,000,000 barrels and the exports about 440,000 barrels. 

Sylvite (KC1) 

Sylvite is isometric, like halite, but the etched figures that may be 
produced on the faces of its crystals indicate a gyroidal symmetry (pen- 
tagonal icositetrahedral class) The habit of the crystals is cubic with 
O(ni) and oo O oo (100) predominating. 

Pure sylvite contains 47 6 per cent Cl and 52 4 per cent K, but the 
mineral usually contains some NaCl and often some of the alkaline sul- 
phates. 

The physical properties of sylvite are like those of halite, except that 
its hardness is 2 and the density i 99 Its melting temperatuie is 738 
and n for sodium light = i 4903 

When heated before the blowpipe the mineral imparts a violet tinge 
to the flame, which can be detected when masked by the yellow flame of 
sodium by viewing it through blue glass Otherwise sylvite and halite 
react similarly. 

Halite and sylvite are distinguished from other soluble minerals by 
the reaction with the bead saturated with copper oxide, and from one 
another by the color imparted to the blowpipe flame. 

Synthesis Sylvite crystals have been made by methods analogous 
to those employed in syntheses of halite crystals 

Occurrence Sylvite occurs associated with halite, but in distinct 
beds, at Stassfurt, Germany, and at Kalusz, Galicia. It has also been 
found, together with the sodium compound, incrusting the lavas of 
Vesuvius. 

Uses. Sylvite Is an important source of potassium salts, large quan- 
tities of which are used in the manufacture of fertilizers, 

CERARGYRITE GROUP 

The cerargyrite group comprises the chloride, bromide and iodide of 
silver. The first two exist as the minerals cerargyrite and bromargyrite, 
both of which crystallize in the isometric system. The isometric Agl 
exists only above 146; below this temperature the iodide is hexagonal. 
The exhagonal modification occurs as the mineral iodyrite, which, of 
course, is not regarded as a member of the cerargyrite group 



138 DESCRIPTIVE MINERALOGY 

Cerargyrite (AgCl) 

Cerargynte, or horn silver, is an important silver ore It is usually 
associated with other silver compounds, the mixture being mined and 
smelted without separation of the components It is usually recog- 
nizable by its waxy, massive character 

Silver chloride consists of 24 7 per cent chlorine and 75 3 per cent 
silver, but cerargynte often contains, in addition to its essential con- 
stituents, some mercury, bromine and occasionally some iodine Crystals 
are rare They are isometric (hexoctahedral class), with a cubical habit, 
their predominant forms being oo O oo (100), oo 0(no), 0(in), 20(221) 
and 202(211) Twins sometimes occur with 0(in) the twinning face 
The mineral is sometimes found massive, embedded among other min- 
erals, but is more frequently in crusts covering other substances 

The fracture of cerargynte is conchoidal The mineral is sectile 
Its hardness is i-i 5 and density about 5 5 Its color is grayish, white 
or yellow, sometimes colorless. On exposure to light it turns violet- 
brown It is transparent to translucent and its streak is white It is a 
very poor conductor of electricity Like halite it is diathermous n for 
sodium, light = 2 071. 

In the closed tube cerargynte fuses without decomposition On 
charcoal it yields a metallic globule of silver, and when heated with oxide 
of copper m the blowpipe flame it gives the chlorine reaction The min- 
eral is insoluble in water and in nitric acid but is soluble in ammonia, and 
potassium cyanide. When a particle of the mineral is placed on a 
sheet of zinc and moistened with a drop of water, it swells, turns black 
and is finally reduced to metallic silver, which, when rubbed by a knife 
blade, exhibits the white luster of the metal. 

Cerargyrite is easily distinguished from all other minerals, except 
the comparatively rare bromide and iodide, by its physical properties and 
by the metallic globule which it yields on charcoal 

Syntheses. Crystals of cerargynte have been obtained by the rapid 
evaporation of ammoniacal solutions of silver chloride, and by the cooling 
of solutions of the chloride in molten silver iodide 

Occurrence The mineral occurs in the upper (oxidized) portions of 
veins of argentiferous minerals, where it is associated with native silver 
and oxidized products of various kinds 

Localities. The most important localities of cerargynte are in Peru, 
Chile, Honduras and Mexico, where it is associated with native silver. 
It is also found near Leadville, Colo*; near Austin, in the Comstock 
lode, Nev., and at the Poorman Mine, and in other mines in Idaho 



CHLORIDES, FLfORIDES, ETC 



139 



and at several places in Utah. Good crystals occur in the Poorman 
Mine. 

Extraction When a silver ore consists essentially of cerargynte the 
metal may be extracted by amalgamation Ores containing compara- 
tively small quantities of cerargynte are smelted 

Production The quantity of cerargyrite mined cannot be safely 
estimated. As has been stated, it is usually wrought with other silver 
ores, 

THE FLUORIDES 

The fluorides are salts of hydrofluoric acid. There are several 
known to occur as minerals, but only two, the fluoride of calcium and 




FIG 60 Group of Fluonte Crystals from Weardale, Co., Durham, England (Foote 

Mineral Company ) 

the double fluorides of sodium and aluminium are of sufficient impor- 
tance to merit description here. 

Fluorite (CaF 2 ) 

Fluorite, or fluorspar, is the principal source of fluorine. It is usually 
a transparent mineral that is characterized by its fine color and its hand- 



140 



DESCRIPTIVE MINERALOGY 



some crystals (Fig 60) Perhaps there is no other mineral known that 
can approach it m the beauty of its crystal groups The uncrystallized 
fluorite may be massive, granular or fibrous 

Fluonte is a compound of Ca and F in the proportion of 48 9 per cent 
F and 51 i per cent Ca Chlorine is occasionally present in minute 
quantities, and SiCfe, AkOs and Fe 2 0s are always present A sample of 
commercially prepared fluonte from Marion, Ky , gave 



CaF 2 
94 72 



Si0 2 

I 22 



CaC0 3 

i 82 



MgO 

68 



The crystallization is isometric (hexoctrahedral class), and inter- 
penetration twins are frequent The principal forms observed are 




FIG 6 1 




FIG 62 



FIG 61 Crystal of Fluonte with oo O oo , 100 (a) and 02, 210 (e). 
FIG 62 Interpeaetration Cubes of Fluonte, Twinned about O(in) 

0(ui), oo O oo (100), oo 02(210) and 462(421) (Fig 61), but some crys- 
tals are highly modified, as many as 58 forms having been identified upon 
the species The twins, with O(ni) the twinning plane, are usually 
interpenetration cubes, or cubes modified on the corners by the octa- 
hedrons (Fig. 62). The mineral occurs also in granular, fibrous and 
earthy masses. 

The cleavage of fluorite is perfect parallel to 0(in). The mineral 
is brittle, its fracture is uneven or conchoidal, its hardness is 4 and its 
density about 3.2. It mdts at 1387. Its color is some shade of yel- 
low, white, red, green, blue or purple, its luster vitreous, and its streak 
is white Many specimens are transparent, some are only translucent. 
Most specimens phosphoresce upon heating A vanety that exhibits a 
green phosphoresence is known as cfdorophane The index of refraction 
for sodium light is 1 43385 at 20. The mineral is a nonconductor of 
electricity. 

The color of the brightly tinted varieties was formerly thought to be 
due to the presence of minute traces of organic substance since it is lost 



CHLORIDES, FLUORIDES, ETC 141 

or changed when the mineral is heated, but recent observations of the 
effect of radium emanations upon light-colored specimens indicate a 
deepening of their color by an increase in the depth of the blue tints. 
This suggests that the coloring matter is combined with the CaF2- It 
may be a colloidal substance 

In the closed tube fluonte decrepitates and phosphoresces When 
heated on charcoal it fuses, colors the flame yellowish red and yields an 
enamel-like residue which reacts alkaline to litmus paper Its powder 
treated with sulphuric acid yields hydrofluoric acid gas which etches 
glass. The same effect is produced when the powdered mineral is fused 
with four times its volume of acid potassium sulphate (HKSO*) in a 
glass tube The walls of the tube near the mixture become etched as 
though acted upon by a sand blast. 

Fluonte is easily distinguished by its cleavage and hardness from 
most other minerals It is also characterized by the possession of 
fluorine for which it gives dear reactions. 

Syntheses Crystals are produced upon the cooling of a molten mix- 
ture of CaF2 and the chlorides of the alkalies, and by heating amorphous 
CaF2 with an alkaline carbonate and a little HC1 in a closed tube at 250. 

Occurrence, Localities and Origin. The mineral occurs in beds, in 
veins, often as the gangue of metallic ores and as crystals on the wails 
of cavities in certain rocks. It is the gangue of the lead veins of northern 
England and elsewhere. Handsome crystallized specimens come from 
Cumberland and Derbyshire, England; Kongsberg, Norway, Cornwall, 
Wales, and from the mines of Saxony. In the United States the mineral 
forms veins on Long Island; in Blue Hill Bay, Maine, at Putney, in 
Vermont; at Plymouth, Conn ; at Lockport and Macomb, in New 
York, at Amelia Court House, Va., and abundantly in southeastern 
Illinois and the neighboring portion of Kentucky, where it occurs asso- 
ciated with zinc and lead ores. These last-named localities, the neigh- 
borhood of Mabon Harbor, Nova Scotia, and Thunder Bay, Lake 
Superior, afford excellent crystal groups. In nature fluonte has been 
apparently produced both by crystallization from solutions and by 
pneumatolytic processes 

Since fluorite is soluble in alkaline waters, its place in the rocks is often 
occupied by calcite, quartz or other minerals that pseudomorph it. 

Uses The mineral is used extensively as a flux in smelting iron and 
other ores, in the manufacture of opalescent glass, and of the enamel 
coating used on cooking utensils, etc It is also used in the manufacture 
of hydrofluoric acid, which, in turn, is employed in etching glass The 
brighter colored varieties are employed as material for vases and the 



142 DESCRIPTIVE MINERALOGY 

transparent, colorless kinds are ground into lenses for optical instruments 
The mineral is also cut into cheap gems, l:no\vn according to color, as 
false topaz, false amethyst, etc Except \\hen used for making lenses or 
as a precious stone, fluorite is prepared for shipment by crushing, wash- 
ing and screening A portion is ground 

Production The fluonte produced in the United States is obtained 
mainly from Illinois and Kentucky, though small quantities are mined 
in Colorado, New Mexico and New Hampshire The production in 
1912 amounted to 116,545 tons, valued at $769,163. Of this, 114,410 
tons came from Illinois and Kentucky. The imports were 26,176 tons, 
valued at $71,616 

THE DOUBLE CHLORIDES AND DOUBLE FLUORIDES 

These double salts are apparently molecular compounds, in which 
usually two chlorides or two fluorides combine, as in AlFa+3NaF 
Moreover, one of the members of the combination of chlorides is nearly 
always either the sodium or the potassium chloride The law of this 
combination is expressed by Professor Remsen in these words " The 
number of molecules of potassium or sodium chloride which combine 
with another chloride is limited by the number of chlorine atoms con- 
tamed m the other chloride " Thus, if NaCl makes double salts with 
MC1 2 , in which M represents any bivalent element, only two are possible, 
viz- MCl 2 +NaCl and MCl 2 +2NaCl With MC1 3 three double salts 
with sodium may be formed, etc These double salts are not regarded 
as true molecular compounds, but they are looked upon as compounds 
in which Cl and F are bivalent like oxygen 

Carnallite (KMgCls 6H 2 0) 

Carnallite may be regarded as a hydrated double chloride of the 
composition MgCk KC1 6H 2 O with 14 i per cent K, 8 7 per cent Mg, 
38 3 per cent Cl and 39 o per cent H 2 It occurs m distinct crys- 
tals but more frequently in massive granular aggregates 

Its crystallization is orthorhombic (bipyramidal class), but the habit 
of its crystals is usually hexagonal because of the nearly equal develop- 
ment of pyramids and brachydomes. Its axial ratio is .5891 i i 3759. 
Crystals are commonly bounded by oo P(no), P(in), JP(ri2), P(ii3), 
oo P eo (oio), 2? a& (021), P 56 (on), |P oa (023), oP(ooi), and P 56 (101). 
The angle no A 3 10=61 2oJ'. 

Carnallite is colorless to milky white, transparent or translucent, 
and has a fatty luster Many varieties appear red in the hand specimens 



CHLORIDES, FLUORIDES, ETC 143 

because of the inclusion of numerous small plates of hematite or goethite, 
or yellow because of inclusions of yelkm liquids or tiny crystals. The 
mineral has a hardness of 1-3, and a density of 1.60 It possesses no 
cleavage but has a conchoidal fracture It is not an electrical conductor. 
It is deliquescent and has a bitter taste Its indices of refraction for 
sodium light are a= i 467, jS= 1.475, 7= 1-494 

Before the blowpipe carnalhte fuses easily. In the closed tube it 
becomes turbid and gives off much water, which is frequently accom- 
panied by the odor of chlorine. It melts in its own water of crystalliza- 
tion. When evaporated to dryness and heated by the blowpipe flame 
a white mass results which is strongly alkaline. The mineral dissolves 
in water, forming a solution which reacts for Mg, K and Cl 

Carnalhte is easily recognized by its solubility, its bitter taste and the 
reaction for chlorine 

Synthesis The mineral separates in measurable crystals from a solu- 
tion of MgCl 2 and KC1 

Occurrence and Origin Carnalhte occurs hi beds associated with 
sylvite, halite, kieserite (p. 246), and other salts that have been pre- 
cipitated by the evaporation of sea water or the water of salt lakes 

Localities It is found in large quantity at Stassfurt, Germany, at 
Kalusz, in Galicia and near Maman, in Persia 

Uses. Carnalhte is used as a fertilizer and as a source of potash 
salts. 

Cryolite (NasAlFe) 

Cryolite usually occurs as a fine-grained granular white mass in 
which are often embedded crystals of light brown iron carbonate (sider- 
ite). The formula given above demands 54 4 per cent F, 12 8 per cent 
Al and 32.8 per cent Na. Analyses of pure white specimens correspond 
veiy closely to this 

The mineral is monoclinic (prismatic class), but crystals are exceed- 
ingly rare and when found they have a cubical habit. Their axial ratio 
is a : b : ^=.9662 : i . i 3882. =89 49'. The principal forms are 
ooP(no), oP(ooi), Pco(oTo), P 00(010) and P 06(100), thus re- 
sembling the combination of the cube and octahedron. Twins are com- 
mon, with oo P(no) the twinning plane 

The deavage of cryolite is perfect parallel to oP(coi). Its fractine 
is uneven. Hardness is 2 5 and density about 3. Its color is snow-white 
inclining to red and brown. Its luster is vitreous or greasy and the 
mineral is translucent to transparent Because of its low index of 
refraction, massive specimens suggest masses of wet snow. The re- 



144 DESCRIPTIVE MINERALOGY 

fractive index /3 for sodium light is i 364 It is a nonconductor of 
electricity. 

Cryolite is very easily fusible, small pieces melting even at the low 
temperature of a candle flame The mineral is soluble in sulphuric acid 
with the evolution of HF When fused in the closed tube with KHS04 
it yields hydrofluoric acid, and -ft hen fused on charcoal fluorine is evolved 
The residue treated with Co(NOs)2 and heated gives the color reaction 
forAl 

By the aid of its reactions with sulphuric acid, its fusibility and its 
physical properties cryolite is easily distinguished from fluonte, which it 
most resembles, and from all other minerals. 

Occurrence, Localities and Origin The occurrences of cryolite are 
very few It has been found in small quantities near Miask in the 
Ihnen Mts, Russia, near Pike's Peak, Colo, and in the Yellowstone 
National Park. Its puncipal occurrence is m a great pegmatitic vein 
cutting granite near Ivigtut, Greenland, whence all the mineral used 
in the arts is obtained The associates of the cryolite at this place are 
sidente, galena, chalcopynte, p^nte, fluonte, topaz and a few rare 
minerals The vein is said to be intrusive into the granite. It is 
believed to be a magmatic concentration 

Uses. Cryolite was formerly employed principally in the manufac- 
ture of alum and of salts of sodium. At present it is used as a flux in 
the electrolytic production of aluminium, and is employed in the man- 
ufacture of white porcelain-like glass, and in the process of enameling 
iron The mineral is quarried in Greenland and imported into the 
United States to the extent of about 2,500 tons annually. Its value is 
about $25 per ton. 

THE OXYCHLORIDES 

The oxychlorides are combinations of hydroxides and chlorides 
Some of them are " double salts " in the sense in which this word is 
explained above. Atacamite is a combination of the oxychlonde 

Cu(OH)Cl with the hydroxide Cu(OH) 2 , or Ncu Cu(OH) 2 . 

Atacamite (Cu(OH)Cl-Cu(OH) 2 ) 

Atacamite is especially abundant in South America The mineral 
is usually found in crystalline, fibrous or granular aggregates of a bright 
green color 

Analyses of specimens from Australia and from Atacama, Chile, yield. 



CHLOEIDES, FLUORIDES, ETC 145 



Cl 


Cu 


CuO 


H 2 


Total 


16 44 


14 67 


5664 


12 O2 


99 77 


IS 83 


14 16 


55 7 


14 31 


IOO 00 



Austraha 
Atacama, Chile. 

The formula lequires 16 6 per cent Cl, 14.9 per cent Cu, 55 8 per cent 
CuO and 12 7 per cent EkO. 

The crystallization of atacamite is orthorhombic (bipyramidal class), 
with a : b : =.6613 : i : .7529 Its crystals are usually slender prisms 
bounded by ooP(no), ooP(i 2 o), ooPoo (oio), P66 (011), oP(ooi) 
and P(III), or tabular forms flattened m the plane of the macropinacoid 
oo P 56 (100). Twins are common, with the twinning plane ooP(no). 

The cleavage of atacamite is perfect parallel to oo P 06 (oio). Its 
fracture is conchoidal. Its hardness is 3-3 5 and density about 3 76. 
Pure atacamite is of some shade of green, varying between bright shades 
and emerald. Its aggregates often contain red or brown streaks or 
grains due to the admixture of copper oxides. It is transparent to trans- 
lucent. The streak of the mineral is apple-green It is a nonconductor 
of electricity Its indices of refraction for green light are a=i 831, 
0= 1.861,7=1 880 

In the closed tube atacamite gives off much water with an acid reac- 
tion, and yields a gray sublimate In the oxidizing flame it fuses and 
tinges the flame azure blue (reaction for copper chloride). It is easily 
reduced to a globule of copper on charcoal and is easily soluble in acids. 

Atacamite is readily distinguished from garmerite, malachite and 
other green minerals by its solubility in acids without effervescence and 
by the azure blue color it imparts to the flame. 

Synthes^s. Crystals have been produced by heating cuprous oxide 
(CugO) with a solution of FeCls, in a closed tube at 250. 

Occurrence, Localities and Origin The mineral is most abundant 
along the west side of the Andes Mountains in Chile and Bolivia. It 
occurs also in South Australia, in India, at Ambriz, on the west coast of 
Afnca, in southern Spain, in Cornwall, where it forms stalactite tubes, 
in southern California, and near Jerome, Arizona. It is formed as the 
result of the alteration of other copper compounds, and is found most 
abundantly in the upper portions of copper veins Atacamite changes 
on exposure to the weather into the carbonate, malachite, and the sili- 
cate, chrysocolla. 

Uses. The mineral is an important ore of copper, but it is mined 
with other compounds and consequently no records of the quantity 
obtained are available. 



CHAPTER VII 
THE OXIDES 

THE oxides (except water) and the hydroxides may be regarded as 
derivatives of water, the hydrogen being replaced wholly or in part 
by a metal. When only part of the hydrogen is replaced an hydroxide 
results, when all of the hydrogen is replaced an oxide results Thus, 
sodium hydroxide, NaHO, may be looked upon as HgO, in which Na has 
replaced one atom of H, and sodium oxide, Na20, as KfeO in which both 
hydrogen atoms have been replaced by this element Ferric oxide and 
ferric hydroxide bear these relations to water: 

H-0 H 



H O H, Fe O Fe, feme oxide, H O Fe, ferric hydroxide 

YFe 2 3 H-0/ Fe(OH) 3 

The oxides constitute a very important, though not a large, class of 
minerals Some of them are among the most abundant of all minerals 
They are separated into the following groups: Monoxides, sesqui- 
oxides, dioxides and higher oxides. 

THE MONOXIDES 

Ice (H 2 O) 

The properties of ice are so well known that they need no special 
description in this place The mineral is never pure, since it contains, 
in all cases, admixtures of various soluble salts. Its crystallization is 
hexagonal and probably trigonal and hemimorphic (ditngonal pyram- 
idal class). Crystals are often prismatic, as when ice forms the cover- 
ing of water surfaces, or the bodies known as hailstones In the form 
of snow the crystals are often stellate, or skeleton crystals, and sometimes 

146 



OXIDES 



147 



hollow prisms The principal forms observed on ice crystals are oP(oooi) 
ooP(ioTo), |P(iol2), P(ioTi) andtfUoli) (Fig 63). 

The hardness of ice is about 1.5 and its density 9181 It is trans- 
parent and colorless except m large masses when it appears bluish. Its 
fracture is conchoidal It possesses no distinct cleavage Its fusing 




FlG. 63 Photographs of Snow Crystals, .Magnified about 15 Diameters (After 

Benttey and Perkins ) 

point is o and boiling point 100. It is a poor conductor of electricity. 
Its indices of refraction for sodium light at 8 are: = 1.3090, = 1.3133. 

COPPER OXIDES 

There are two oxides of copper, the red cuprous oxide (Cu2O) and 
the black cupric oxide (CuO). Both are used as ores, the former being 
much more important a source of the metal than the latter 

Cuprite (Cu 2 O) 

Cuprite occurs in crystals, in granular and earthy aggregates and 
massive The mineral is usually reddish brown or red and thus is easily 
distinguished from most other minerals. Its composition when pure is 
88.8 per cent Cu and n 2 per cent O. 

In crystallization the mineral is isometric, in the gyroidal hemihedral 
division of the system (pentagonal icositetrahedral dass). Its pre- 



148 DESCRIPTIVE MINERALOGY 

dominant forms axe ooOoo(ioo), 0(iu), ooO(uo), 0002(210), 
202(211), 20(221) and 301(321), sometimes lengthened out into 
capillary crystals, producing fibrous varieties (var chdcotr^ch^te). 

The cleavage of cupnte is fairly distinct parallel to O(in) Its frac- 
ture is uneven or conchoidal Its hardness is 3 5-4 and density about 6 
The mineral is in some cases opaque, oftener it is translucent or even 
transparent in very thin pieces By reflected light its color is red, 
brown and occasionally black. By transmitted light it is crimson When 
gently heated transparent varieties turn dark and become opaque, but 
they reassume their original appearance upon cooling. Its streak is 
brownish red and has a brilliant luster When rubbed it becomes yellow 
and finally green. The luster of the mineral vanes between earthy and 
almost vitreous It is a poor conductor of electricity, but its con- 
ductivity increases rapidly with using temperature. Its refractive index 
for yellow light = 2.705 

In the blowpipe flame cuprite fuses and colors the mantle of the 
flame green If moistened with hydrochloric acid before heating the 
flame becomes a brilliant azure blue. On charcoal the mineral first 
fuses and then is reduced to a globule of metallic copper. It dissolves in 
strong hydrochloric acid, forming a solution which, when cooled and 
diluted with cold water, yields a white precipitate of cuprous chloride 
(Cu 2 Cl 2 ). 

Cupnte may easily be distinguished from other minerals possessing 
a red streak by the reaction for copper such as the production of a 
metal globule on charcoal, and the formation of cuprous chloride in con- 
centrated hydrochloric acid solutions by the addition of water. More- 
over, the mineral is softer than hematite and harder than reaglar, cin- 
nabar and proitsttte. 

Cuprite suffers alteration very readily. It may be reduced to native 
copper, in which case the copper pseudomorpbs the cuprite, or, on ex- 
posure to the air it may be changed into the carbonate, malachite, 
pseudomorphs of which after cupnte are common. 

Syntheses Crystals of cupnte have frequently been observed on 
copper utensils and coins that had been buried for long periods of time. 
Crystals have also been obtained by long-continued action of NHs upon 
a mixture of solutions of the sulphates of iron and copper, and by heating 
a solution of copper sulphate and ammonia with iron wire in a dosed tube 

Occurrence^ Origin and Localities Cuprite often occurs as well 
defined crystals embedded in certain sedimentary rocks in the upper, 
oxidized portions of copper veins, and in masses m the midst of other 
copper ores, from which it was produced by oxidation processes* It is 



OXIDES 149 

found as crystals in Thuringia, in Tuscany, on the island of Elba, in 
Cornwall, Eng , at Chessy, France, and near Coquimbo, in Chile. 
In Chile, m Peru, and in Bolivia it exists in great masses 

In the United States it occurs at Cornwall, Lebanon Co , Penn. It 
is also found associated with the native copper on Keweenaw Point, 
Mich , at the copper mines in St. Genevieve Co , Mo ; at Bisbee and 
at other places in Arizona The fibrous vanety known as chalcoinchite 
is beautifully developed at Morenci in the same State. 

Uses Cuprite is mined with other copper compounds as an ore of 
copper. 

Melaconite, or Tenorite (CuO) 

Melaconite, or tenonte, is less common than cuprite. It usually 
occurs in massive forms or in earthy masses Crystals are rare Its 
composition is 79 8 per cent Cu and 20 2 per cent 0. 

In crystallization melacomte is tnchnic with a monochnic habit. 
Its axial ratio is a : b : c=i 4902 : i : 1 3604 and =99 32'. The 
angles a and 7 are both 90, but the optical properties of the crystals 
proclaim their tnchnic symmetry. 

The mineral possesses an easy cleavage parallel to oP(ooi). Its frac- 
ture is conchoidal and uneven, its hardness 3 to 4 and density about 6. 
When it occurs in thin scales its color is yellowish brown or iron gray. 
When massive or pulverulent it is dull black. Its streak is black, chang- 
ing to green when rubbed. Its refractive index for red light is 2 63. 
It is a nonconductor of electricity. 

The chemical reactions of melaconite are precisely like those of cu- 
pnte, with the exception that the mineral is infusible. 

Melaconite is distinguished from the black minerals that contain no 
copper by its reaction for this metal It is distinguished from covelhte 
and other dark-colored sulphides containing copper by its failure to give 
the sulphur reaction. 

Syntheses Crystals of melaconite have been found in the flues of 
furnaces in which copper compounds and moist NaCl are being treated. 
They have also been obtained by the decomposition of CuCk by water 
vapor 

Occurrence, Localities and Origin. The mineral usually occurs associ- 
ated with other ores of copper, from which it has been formed, in part 
at least, by decomposition. It is mined with these as jmt ore. Thin 
scales are found on the lava of Vesuvius, where it must have been f onned 
by sublimation. Masses occur at the copper mines of Ducktowu, Temi. 




150 DESCRIPTIVE MINERALOGY 

Zincite (ZnO) 

Zincite is the only oxide of the zinc group of elements known It is 
rarely found in crystals It usually occurs m massive forms associated 
with other zinc compounds. 

Pure zmcite is a compound containing 80 3 per cent Zn and 19 7 per 
cent 0, Since, however, the mineral is frequently admixed with man- 
ganese compounds it often contains also some manganese and a little 
iron. A specimen from Sterling Hill, N J , 
gave 98 28 per cent ZnO, 6 50 per cent MnO 
and 44 per cent Fe20g 

Natural crystals of zmcite are very rare 
From a study of artificial crystals it is known 
that the mineral is hexagonal and hemimorphic 
(dihexagonal pyramidal class). The principal 
forms observed are ooP(ioTo), ooP2(ii2o), 
oP(oooi), P(ioTi), P2(ii22) and various other 
Fro. 64 Zincite Crystal pyramids of the ist and 2d orders Their habit 
with oop, iolo (m). 1S hemimorphic with P(iori) and oP(oooi) at 
p, roll (p) and oP, ^ op p OS i te ends of a short columnar crystal 
0001 W (Fig. 64) 

The cleavage of ^incite is perfect parallel to oP(oooi) Its fracture 
is conchoidal, its hardness 4-4 5 and density about 5 8 Although color- 
less varieties are known, the mineral is nearly always deep red or orange- 
yellow, due most probably to the manganese present in it The streak 
of the red varieties is orange- yellow. Its indices of refraction are 
about 2 The mineral is a conductor of electricity. 

When heated in the closed tube the common variety of zmcite 
blackens, but it resumes its original color on cooling With the borax 
bead it gives the manganese reaction Heated on charcoal it coats the 
coal with a white film, which, when moistened with cobalt solution and 
heated again with the oxidizing flame of the blowpipe, turns green The 
mineral dissolves in acids 

When exposed to the atmosphere zmcite undergoes slow decomposi- 
tion to zinc carbonate 

Syntheses Zinc oxide crystals are frequent products of the roasting 
of zinc ores in ovens They have also been produced by the action of 
zinc chloride vapor upon lime and by the action of water upon zinc 
chloride at a red heat. 

Occurrence and Locafofoes The mineral occurs only in a few places 
It is found with other zinc and manganese minerals near Ogdensburg, 



OXIDES 151 

and at Franklin Furnace, m Sussex Co , N J , m the form of great 
layers in marble, that are bent into troughs The lajers are probably 
veins that were filled from below by emanations from a great underground 
reservoir of igneous rock 

Uses Most of the zmcite produced in the United States is used in 
the manufacture of zinc oxide The ore, which consists of a mixture of 
zincite, franklimte (see p 199), and willemite (see p 306), is crushed 
and separated into its component parts by mechanical processes The 
separated zmcite is then mixed with coal and roasted The zinc oxide 
is volatilized and is caught m tubes composed of bagging. The willemite 
and franklimte are smelted to metallic zinc and the residues are used m 
the manufacture of spiegeleisen 

Production Formerly this mineral, together TMth the silicate found 
associated with it in New Jersey, constituted the most important source 
of zinc in this country At present most of the metal is obtained from 
sphalerite Of the 380,000 tons of zinc in spelter and zinc compounds 
produced in the United States during 1912 about 69,760 tons were 
made from zmcite and the ores associated with it. This had an esti- 
mated value of $9,626,991. 

THE SESQUIOXIDES 

The sesquioxides (R20s) include a few compounds of the nonmetals 
that are comparatively rare and a group of metallic compounds that 
includes two minerals of great economic importance. One of these, 
hematite (FeaOa), is the most valuable of the iron ores 

ARSENOLITE CLAUDETITE GROUP 

The only group of the nonmetallic sesquioxides that need be referred 
to in this place comprises those of arsenic and antimony. This is an 
isodimoiphous group including four minerals. 

Isometric Monochmc 

Arsenohte As20s Claudetite 

Senarmoutote Sb20s Valenttmte 

All the minerals of the group are comparatively rare. The isometric 
forms occur in well developed octahedrons and in crusts covering other 
minerals They are also found in earthy masses. It is probable that at 
high temperatures the isometric forms pass over into the monodinic 
modifications, as some of the latter have been abserved to consist of 
aggregates of tiny octahedrons. Crystals of daudetite are distinctly 



152 DESCRIPTIVE MINERALOGY 

monoclinic, but they are so thinned as to possess an orthorhombic 
habit Valentmite crystals, on the contrary, appear to be plainly 
orthorhombic, but their apparent orthorhombic symmetry may be 
due to submicroscopic twinning of the same character as that in 
claudetite, but which in the latter mineral is macroscopic 

All four minerals occur as weathered products of compounds contain- 
ing As or Sb They give the usual blowpipe reactions for As or Sb 
In the closed tube they melt and sublime 

Arsenolite (As2Os) is colorless or white Its specific gravity is 3,7 
and refractive index for sodium light = i 755 It usually occurs in octa- 
hedrons, or m combinations of 0(in) and ooO(no), but these when 
viewed in polarized light are often seen to be amsotropic The mineral is 
found also in aggregates of hair-like crystals with a hardness of i 2 It is 
soluble in hot water, yielding a solution with a sweetish taste 

Senarmonite (SbgOs) is gray or white Its density is 5 2 and 
n=2 087 for yellow light Its octahedral crystals are also often aniso- 
tropic, its hardness=2 It is soluble in hot HC1 but is only very 
slightly soluble in water When heated it turns yellow, but becomes 
white again upon cooling 

Claudetite (As2Os) is monochmc prismatic, with a : b : c= 4040 : i 

: 3445 and /3=86 03' Its white crystals are usually tabular parallel 

to oo P ao (oio) and are twinned, with oo P 56 (100) the twinning plane 

Their cleavage is parallel to oo P o> (oio) and their density is 4 15 

H= 2.5 The mineral is an electrical nonconductor 

Valentinite (Sb2Os) is apparently orthorhombic bipyramidal (pos- 
sibly monoclimc prismatic) with a : b : c= 3914 i 3367 Its crystals 
are tabular or columnar in habit and are very complex The mineral is 
found also in radial groups of acicular crystals and m granular and 
dense masses Its color is white, pink, gray or brown, and streak 
white Its density is 5 77 and hardness 2 5-3. It is insoluble in HC1 
It is a nonconductor of electricity 

CORUNDUM GROUP 
t 

The sesquioxides of aluminium and iron constitute an isomorphous 
group crystallizing in the rhombohedral division of the hexagonal sys- 
tem (ditngonal scalenohedral class) Both the aluminium and iron 
compounds, corundum and hematite^ are of great economic importance 



OXIDES 



153 



Hematite (Fe20a) 

Hematite is one of the most important minerals, if not the most 
important one, from the economic standpoint, smce it is the most val- 
uable of all the iron ores It is known by its dark color and its red 
powder It occurs in black, glistening crystals, in yellow, brown or red 
earthy masses, in granular and micaceous aggregates and in botiyoidal 
and stalactitic forms 

Chemically, the mineral is Fe 2 0a corresponding to 30 per cent and 
70 per cent Fe. In addition to these constituents, hematite often con- 
tains some magnesium and some titanium. By increase in the latter 
element it passes into a mineral which has not been distinguished from 
ilmenite (see p 462) 

The habit of hematite crystals is nearly always rhombohedraL 




FIG* 65 Hematite Crystals with R, loTi (r), |P 2 , 2243 (*), JR 1014 (), oop 2l 
1 1 20 (0) and oR, oooi (c) 

Their axial ratio is a : c=i : 1.3658, and the predominant forms are 
R(ioTi), iR(iol4), ^2(2243), the prisms oo P(ioTo) and ooP2(ii2o) 
and often the basal plane (Fig. 65) In addition, about no other forms 
have been identified The crystals are often tabular, and sometimes 
are grouped into aggregates resembling rosettes. In many cases the 
terminal faces are rounded A parting is often observed parallel to 
the basal plane, due to the occunence of the mineral in aggregates in 
which each crystal is tabular. 

Hematite has no well defined cleavage Its fracture is conchoidd or 
earthy. Its crystals are black, glistening and opaque, except in very 
small splinters These are red and transparent or translucent. Earthy 
varieties are red. The streak of all varieties is brownish red or cherry- 
red. The hardness of the crystallised hematite is 5.5-6.5 aad its density 
about 5.2. It is a good conductor of electricity. Its refractive indices 
are: 60=3.22, 6=2.94 for yellow light. 

The mineral is infusible before the blowpipe. In the reducing flame 
on charcoal it becomes magnetic, and when heated with soda it is reduced 
to a magnetic metallic powder It is soluble IB strong hydrochloric acid. 



154 DESCRIPTIVE MINERALOGY 

The crystalline and earthy aggregates of hematite to which distinct 
names have been given are 

Specular, when the aggregate consists of grains with a glistening, 
metallic luster, like the luster of the crystals When the grains are thin 
tabular the aggregate is said to be micaceous 

Columnar or fibrous, when in fibrous masses The color is usually 
brownish red and the luster dull The botryoidal, stalactic and various 
imitative forms belong here Red hematite is a compact red variety in 
which the fibrous structure is not very pronounced 

Red ocher is a red earthy hematite mixed with more or less clay and 
other impurities 

Clay ironstone is a hard brownish or reddish variety with a dull luster 
It is usually a mixture of hematite with sand or clay 

Oolitic ore is a red variety composed of compacted spherical or nearly 
spherical grams that have a concentric structure 

Fossil ore differs from oolitic ere mainly in the fact that there are 
present in it small shells and fragments of shells that are now composed 
entirely of hematite 

Martite is a pseudomorph of hematite after magnetite. 

Hematite is distinguished from all other minerals by its red powder 
and its magnetism after roasting 

Syntheses Crystals of hematite are obtained by the action of steam 
on ferric chloride at red heat, by heating ferric hydroxide with water 
containing a trace of NH*F to 250 in a closed tube, and by cooling a 
solution of Fe20s in molten borax or halite 

Occurrence and Origin Hematite is found in beds with rocks of 
nearly all ages It occurs also as a deposit on the bottoms of marshy 
ponds, and m small grams m the rocks around volcanic vents The 
crystallized variety is often deposited on the sides of clefts in rocks near 
volcanoes and on the sides of certain veins It is produced by sublima- 
tion, by sedimentation and by metasomatic processes 

Localities Handsome crystals occur on the island of Elba, near 
Limoges in France, m and on the lavas of Vesuvius and Etna, at many 
places in Switzerland, Sweden, etc , and at many in the United States 

Beds of great economic importance occur m the Gogebic, Menommee 
and Marquette districts in Michigan; m the Mesabe and Vermilion 
districts in Minnesota, m the Pilot Knob and Iron Mountain districts 
in Missouri, and in the southern Appalachians, especially m Alabama 

Uses. In addition to its use as an ore the fibrous variety of hematite 
is sometimes cut into balls and cubes to be worn as jewelry. The earthy 
varieties are ground and employed in the manufacture of a dark red 



OXIDES 155 

paint such as is used on freight cars, and the ponder of some of the mass- 
ive forms is used as a polishing ponder 

Prodtiction.Most of the iron ore produced in the United States is 
hematite, and by far the greater proportion of it comes from the Lake 
Superior region The statistics for 191 2 follow 

QUANTITY (IN LONG TONS) OF IRON ORE MINED IN THE SEVERAL LEAD- 
ING STATES DURING 1912 

Hematite Other Iron Ores Total 

Minnesota ..... 34j43i,oo . . 34,431,000 

Michigan ..... 11,191,000 11,191,000 

Alabama . . . 3,814,000 749,ooo 4,563,000 

New York . 106,327 1,110,000 1,216,327 

Wisconsin 860,000 860,000 

Tennessee. 246,000 171,000 417,000 

Total in U S . 51,345,782 3,804,365 55,150,147 

The total production in 1912 was valued at about $104,000,000 
Corundum 



Corundum is the hardest mineral known, with the exception of dia- 
mond In consequence of its great hardness an impure variety is used 
as an abrading agent under the name of emery. It is also one of the 
most valuable of the gem minerals It occurs as crystals and in granular 
masses 

The mineral is nearly always a practically pure oxide of aluminium of 
the composition AkOs, in which there are 52 9 per cent Al and 47 i per 
cent O The impure varieties usually contain some iron, mainly as an 
admixture in the form of magnetite 

The axial ratio of corundum crystals is i : i 36 The forms are 
usually simple pyramids, among which |P2(2243) and |P2(44S3) 
are the most common (Fig. 66), and the prism oo P2(ii2o) The basal 
plane is also common (Fig 67). Many crystals consist of a series of 
steep prisms and the basal plane, with a habit that may be described as 
barrel-shaped (Fig 68) The crystals are often rough with rounded 
edges The prismatic and pyramidal faces are usually striated hori- 
zontally, and the basal plane by lines radiating from the center 

All corundum crystals are characterized by a parting parallel to the 
basal plane, and often by a cleavage parallel to the rhoinbohedron, due 
to the presence of lamellae twinned parallel to R(ioli). The fracture 
o the mineral is conchoidal or uneven. Its density is about 4 and its 



156 



DESCRIPTIVE MINERALOGY 



hardness 9 The mineral possesses a vitreous to adamantine luster It 
is transparent or translucent Its streak is uncolored Its color varies 
from white, through gray to vanous shades of red, yellow, or blue 
The blue varieties are pleochroic in blue and greenish blue shades The 
mineral is a nonconductor of electricity. Its refractive indices for 
yellow light are w=i 7690, =i 7598. 

Three varieties of corundum are recognized in the arts: Sapphire, 
corundum and emery 

Sapphire is the generic name for the finely colored, transparent or 
translucent varieties that are used as gems, watch jewels, meter bearings, 
etc. The sapphires are divided by the jewelers into sapphires, possessing 






FIG 66 



FIG 67 



FIG 68 



FIG 66 Corundum Crystal with |P2, 4483 (u) 

Fee. 67 Corundum Crystal with R, loYi (r), oPs, 1120 (a), and oR, oooi (c) 
FIG. 68 Corundum Crystal Form a, v and c as in previous figures Also P 2 , 
2243 (n) and 2R, 0221 ($) 

a blue color, rubies, possessing a red shade, Oriental topazes, Oriental 
emeralds and Oriental amethysts having respectively yellow, green and 
purple tints. 

Corundum is the name given to dull colored varieties that are ground 
and used as polishing and cutting materials 

Emery is an impure granular corundum, or a mixture of corundum 
with magnetite (FeaO^) and other dark colored minerals Emery, like 
corundum, is used as an abrasive. It is less valuable than corundum 
powder because it contains a large proportion of comparatively soft 
material 

Powdered corundum when heated for a long time with a few drops of 
cobalt nitrate solution assumes a blue color The mineral gives no 
definite reaction with the beads It is infusible and insoluble. It is 



OXIDES 157 

most easily recognized by its hardness The mineral alters to spinel 
(p 196) and to fibrous and platy aluminous silicates 

Syntheses Corundum crystals have been produced artificially in 
many different ways, but only recently has the manufacture of the gem 
variety been accomplished on a commercial scale Amorphous Al 2 Cs 
dissolves in melted sodium sulphide and crystallizes from the glowing 
mass at a red heat By melting Al 2 0s in a mass of some fluoride and. 
potassium carbonate containing a little chromium, and using~compara- 
tively large quantities of material, violet and blue rubies were obtained 
by Fremy and Verneuil Rubies are also produced by melting AfaOs 
and a little C^Os for several minutes at a temperature of 2250 C in 
an electric oven 

In recent years reconstructed rubies have become a recognized article 
of commerce These are crystalline drops of ruby material made by 
melting tiny splinters and crystals of the mineral in an electric arc 

Alundum is an artificial corundum made by subjecting the aluminium 
hydroxide, bauxite, to an intense heat (5ooo-6ooo) m an electric 
furnace. 

Occurrence and Origin Corundum usually occupies veins in crys- 
talline rocks or is embedded in basic intrusive rocks and in granular 
limestone The sapphire varieties are also often found as partially 
rounded crystals in the sands of brook beds The varieties found in 
igneous rocks are primary crystallizations from the magmas producing 
the rocks. The varieties in limestones are the result of metamorphic 
processes 

Localities Sapphires are obtained mainly from the limestone of 
Upper Burma They are known also to occur in Afghanistan, in Kash- 
mir and in Ceylon They are occasionally found in the diamond-bearing 
gravels of New South Wales and in the bed of the Missouri River, near 
Helena, Montana In the United States sapphire is mined near the 
Judith River in Fergus Co , and in Rock Creek in Granite Co., Mont., 
where it occurs in a dike of the dark igneous rock known as monduquite, 
and is washed from the placers of three streams in the same State. The 
only southern mines that have produced gem material are at Franklin 
and Culsagee, N. C , and from these not any great quantity of stones of 
gem quality have been taken 

The largest sapphire crystal ever found was taken, however, from 
one of them It weighs 312 Ib , is blue, but opaque. From one of 
these mines, also, came the finest specimen cf green sapphire (Oriental 
emerald) ever found 

Corundum in commercial quantities occurs on the coast of Malabar, 



158 DESCRIPTIVE MINERALOGY 

m Siam, near Canton, China, and in southeastern Ontario, Canada. 
Emery is obtained from several of the Grecian Islands, more particularly 
Naxos, and from Asia Minor It is mined in the United States at Chester, 
Mass, and at Peekskill, N Y Crystallized corundum occurs near 
Litdxfield, Conn , at Greenwood, Maine, at Warwick and Amity, N Y , 
at Mineral Hill, Penn , m Patrick Co , Va , at Corundum Hill and at 
Laurel Creek, Macon Co., N C , and at \ anous points in Georgia, at 
all of which places it has been mined In all the localities within the 
United States the corundum occurs on the peripheries of masses of 
pendotite (ohvine rocks) 

Uses Corundum, emery and alundum, after crushing and washing, 
are used as abrasives and m the manufacture of cutting wheels. 

Production. The amount of sapphire produced in the United States 
m 1912 was valued at $195,505 Most of it was used for mechanical 
purposes, but 384,000 carats were used as gem material 

Most of the corundum used in the United States is imported from 
Canada, where it occurs in Hakburton, Renfrew and neighboring coun- 
ties in Ontario, as crystals scattered through the coarse-grained crys- 
talline rocks known as syenite, nephelme syenite and anorthosite 

Most of the emery is also imported Only 992 tons with a value 
of $6,652 were mined in 1912 The imports of corundum and emery 
were valued at $501,725, but the importation of these substances is 
gradually diminishing because of the rapid increase in the amounts 
of alundum and carborundum manufactured In 1912 the production 
of alundum reached 13,300,000 Ib valued at $796,000, 

THE DIOXIDES 

THE KONMETALLIC DIOXIDES 

There are but few dioxides of the nonmetals that occur as minerals, 
and only one of these, quartz, is abundant 

SILICA GROUP 

Silica (SiOa) occurs in nature in four or five important modifica- 
tions as follows. 

a Qmrtz, tngonal-trapezohedral class, below 575. 

j8 Quartz, hexagonal-trapezohedral class, above 575 and below 870 

Tridymite, rhombic bipyramidal, pseudohexagonal habit. Hex- 
agonal above 117. 

Cristobdite, tetragonal system, pseudocubic habit Isometric above 
140. 



OXIDES 



159 



Chalcedony is regarded by many mineralogists as a form of quartz, 
but its index of refraction for red light is n=i 537, which is noticeably 
lower than that of either ray in quartz, which is i 5390, e=i 5480 
for the same color Its hardness also is a little less than that of quartz. 
Some mineralogists believe that all of these properties may be explained 
on the assumption that the mineral is a mass of fine quartz fibers, perhaps 
mixed with other substances, but those \vho have investigated it by 
high temperature methods are inclined to regard it as a distinct mineral 

Quartz (Si0 2 ) 

Quartz vies with calcite for the commanding position among the 
minerals It is very abundant, and appears under a great variety of 





FIG 69 



FIG 70. 



FEG 69 Quartz Crystal Exhibiting Rhombohedral Symmetry R, loir (r), R, 

oili (s) and R, loTb (m) 

FIG 70 Ideal (A) and Distorted (B) Quartz Crystals Bounded by same Forms as 

m Fig 69 

forms Often it occurs in distinct crystals At other times it appears 
as grains without distinct crystal forms, and again it constitutes great 
massive deposits 

Pure quartz consists of 46 7 per cent Si and 53.3 per cent (X Mass- 
ive varieties often contain, in addition, some opal (Si(OH)4), and traces 
of iron, calcite (CaCOs), clay, and other impurities 

The crystallization of quartz is in the trapezohedral tetartohedral 
division of the hexagonal system (trigonaUrapezohedral class), at tem- 
peratures below 575. When formed above this temperature its sym- 
metry is hexagonal trapezohedral (hemihedral). The former is known as 
a. quartz, and the latter as jS quartz. They readily pass one into the 
other at the stated temperature. The axial ratio is i : i.i. The prin- 

_ _ 2P2 

cipal forms observed are +R(ioii), -R(om), oo R(ioio), (1121), 



160 



DESCRIPTIVE MINERALOGY 



(Fig 74) and a series of steep rhombohedrons and trapezo- 
hedrons Although these may all be tetartohedral since t he geometrical 





FIG 71 Etch Figures on Two Quartz Crystals of the Same Form, Illustrating Dif- 
ferences in Symmetry \ Right-Hand Crystal B Left-Hand Crystal 
(After Penfidd ) 




FIG 72 Group of Quartz Crystals with Distorted Rhombohedral Faces (Foote 

Mineral Company ) 

forms of the first four are not distinguishable from the corresponding 
hemihedral ones, the crystals possess a rhombohedral symmetry (Fig. 
69). The angle ioTiA"iioi = 85 46' 



OXIDES 



161 



Often the +R and the -R faces are equslly de\ eloped so that they 
appear to belong to the hexagonal pyramid P (Fig yoA) Their true 
character, ho\\ever, is clearly brought out by etching, when figures are 
produced on the +R and the -R that are differently situated with 
respect to the edges of the faces (Fig 71) On the other hand, on many 
crystals some of the R faces are very much enlarged at the expense of 
the others (Fig 72) 

The crystals are commonly pnsmatic Often they are so dis- 





FIG 73 FIG 74 

FIG 73 Tapenng Quartz Crystal with Rhombohedral Symmetry \ Combination 

of r, z, m and Two Steep Rhombohedrons B Cross-section near Top. 
FIG 74 Quartz Crystals Containing ooR, iolo (m), R, loll (r), R, oiTi (s), 

), r, 510*1 (*) 



and /, sin 

2 

onB 



), -/, sT6"i (*) on A, and r, 1121 

2 2 



torted that it is difficult to detect the position of the c axis (Fig 
708) The stnations on oo R(ioTb) are, however, always parallel to 
the edges between R and ooR When these are sharply marked the 
position of the vertical axis is easily recognized Many crystals 
taper sharply toward the ends of the c axis This tapering is due to 
oscillatory combination of the prism ooR with rhombohedrons 

(Fig- 73)- 

The habits of the crystals vary with the crystallization of the quartz. 
On crystals of the phase the +R and R faces are equally developed 
and trigonal trapezohedrons are absent. The crystals are hexagonal in 



162 



DESCRIPTIVE MINERALOGY 



habit Crystals of the a phase usually exhibit marked differences in 
the size and character of the rhombohedral planes, and trigonal trape- 
zohedrons may be present on them Such crystals are usually trigonal 
in habit and prismatic 

The small (1121) faces on all types of crystals (Fig 74) are 

2 

always striated parallel to the edge between this plane and +R. By 
their aid the +R can always be distinguished from the R This is a 
matter of some practical importance since plates cut from quartz crystals 
possess the power of rotating a ray of polarized light. The plates cut 






C D 

FIG 75 Supplementary Twins of Quartz 

C is a combination of A and B in Fig 74 twinned about *> P2(ii2o) This is 
known as the Brazil law 

D is a combination of two crystals like B twinned about c as the twinning axis 
One is revolved 60 with reference to the others, thus causing the r and s faces to 
fall together Swiss law E is a twin like D, showing portions of planes belonging 
to each individual It contains also the form s. 



from some crystals turn the ray to the right; those cut from others turn 
it to the left Crystals that produce plates of the first kind are known 
as right-handed crystals, those that produce plates of the second kind as 
left-handed crystals. Since this property of quartz plates is employed 
in the construction of optical instruments for use m the detection of 
sugars and certain other substances in solution it is important to be 
able to distinguish those crystals that will yield right-handed plates from 
those that will yield left-handed ones Observation has shown that 



_ 

when the - (1121) faces are in the upper right-hand corner of the oo R 

plane immediately beneath +R the crystal is right-handed When 
these faces are in the upper left-hand corner of this oo R plane the crystal 



OXIDES 163 



is left-handed In either case, when (5i5i) is present it occurs 

4 

2 p 2 
between -- (1121) and the oo R face beneath +R 

Interpenetration t\\ms of quartz are so common that few crystals 
can be observed that do not exhibit some evidence of thinning (Fig 75). 
The twinning plane is oo R, so that the c axes in the twinned individuals 
are parallel and, indeed, often coincident The R faces and the oo R 
faces practically coincide in the twinned parts so that the crystals 
resemble untwinned ones The twinning is exhibited by dull areas of 
R on bright areas of +R faces and by breaks in the continuity of the 
striations on oo R 

Other twinning laws have also been observed in quartz, but their 
discussion as well as the more complete discussion of the mineral's 
crystallization must be left for larger treatises In the most common of 
these other laws the individuals are thinned about 
P2(ii22). See Fig 76 

The fracture of quartz is conchoidal Its hard- 
ness is 7 and density 2 65 Its luster is \itreous, or 
sometimes greasy Pure specimens are transparent 
or colorless, but most varieties are colored by the 
addition of pigments or impurities When the 
coloring matter is opaque it may be present in 
sufficient quantity to render the mineral also opaque ^ 

on. i IT- * j r FlG 76 Quart! 

The streak is colorless in pure varieties, and of some xwmned about 
pale shade in colored varieties. The mineral is pyro- p 2 (n22) 
electric and circularly polarizing as described above 
It is an electric insulator at ordinary temperatures Its refractive 
indices for yellow light are: o>= i 5443, = i 5534 

Quartz resists most of the chemical agents except the alkalies. It 
dissolves in fused sodium carbonate and in solutions of the caustic 
alkalies It is also soluble in HF and to a very slight degree in water, 
especially in water containing small quantities of certain salts When 
heated to 575 the a variety passes into the /3 variety, at 870 both 
varieties pass into tndymite, and at 1470 the tndymite passes over into 
cristobahte. Gradual fusion occurs just below 1470. 

The varieties of quartz have received many different names depend- 
ing largely upon their color and the uses to which they are put. They 
may be grouped for convenience into crystallized and crystalline vari- 
eties 

The principal crystallized varieties are: 




164 DESCRIPTIVE MINERALOGY 

Rock crystal, the colorless, transparent variety, that often forms 
distinct crystals This is the variety that is used in optical instruments 
It includes the Lake George diamonds, rhmestones and Brazilian peb- 
bles 

Amethyst, the violet-colored transparent variety. 

Rose quartz, the rose-colored transparent variety. 

Citrine or false topa~, a yellow and pellucid kind 

Smoky quartz or Cairngorm stone, a smoky yellow or smoky brown 
variety that is often transparent or translucent, but sometimes almost 
opaque. 

The last four varieties are used as gems, the Cairngorm stone being a 
popular stone for mourning jewelry 

M^lky quartz is the white, translucent or opaque variety such as so 
commonly forms the gangue m mineral veins and the material of " quartz 



Sag&mte is rock crystal including acicular crystals of rutile 

Aventurine is rock crystal spangled with scales of some micaceous 
mineral 

The puncipal crystalline varieties are 

Chalcedony , a very finely fibrous, transparent or translucent waxy- 
looking quartz that forms mamillary or botryoidal masses Its color is 
white, gray, blue or some other delicate shade The water that is always 
present in it is believed to be held between the minute fibers, and not to 
be combined with the silica (see also p 159) 

Carnehan is the name given to a clear red or brown chalcedony 

Chrysoprase is an apple-green chalcedony 

Prase is a dull leek-green variety that is translucent 

Plasma differs from prase in having a brighter green color and in 
being translucent 

Heliotrope, or lloodstone, is a plasma dotted with red spots of jasper. 

All of the colored chalcedonies are used as gems or as ornamental 
stones 

Agate is a chalcedony, or a mixture of quartz and chalcedony , vane- 
gated in color The commonest agates have the colors arranged in 
bands, but there are others, like " fortification agate " in which the 
colors are irregularly distributed, and still others in which the variation 
in color is due to visible inclusions, as in " moss-agates " The different 
bands in banded agates often differ in porosity. This property is taken 
advantage of to intensify the contrast in their colors The agate is 
soaked in oil, or in some other substance, and is then treated with chem- 
icals that act upon the material absorbed by it Those bands which 



OXIDES 165 

have absorbed the greater quantity of this material become darker in 
color than those that have absorbed less 

On) % is a very evenly banded agate in which there is a marked con- 
trast in colors Cameos are onyxes in one band of which figures are cut, 
leaving another band to form a background 

Sardonyx is an onyx in which some of the bands consist of carnelian. 
It is usually red and white. 

Flint, jasper, hornstone and touchstone are very fine grained crystalline 
aggregates of gray, red or nearly black mixture of opal, chalcedony and 
quartz They are more properly rocks than minerals Chert is an im- 
pure flint 

Sandstone is a rock composed of sand grains, most of tthich are 
quartz, cemented by clay, calcite or some other substance. When the 
cement is quartz the rock is a quartzite Oilstones, honestones and some 
whetstones are cryptocrystalhne aggregates of quartz, very dense and 
homogeneous, except for tiny rhombohedral cavities that are thought to 
have resulted from the solution of crystals of calcite They are gener- 
ally believed to be beds of metamorphosed chert 

Syntheses Crystallized quartz has been made in a number of ways, 
both from superheated aqueous solutions and from molten magmas 
Crystals have been produced by the action of water containing am- 
monium fluoride upon powdered glass and upon amorphous Si02, and 
by heating water in a dosed glass tube to high temperatures The 
separation of crystals from molten magmas is facilitated by the addition 
of small quantities of a fluoride or of tungsten compounds. 

Occurrence and Origin Quartz occurs as an essential constituent of 
many crystalline rocks such as granite, gneiss, etc., and as the almost sole 
component of certain sandstones It constitutes the greater portion of 
most sands and the material of many veins. It also occurs as pseudo- 
morphs after shells and other organic bodies embedded in rocks, having 
replaced the original substance of which these bodies were composed. 
It is also one of the decomposition products of many silicates. It may 
thus be primary or secondary in origin. It may result from igneous or 
aqueous processes, or it may be a sublimation product. 

Localities Quartz is so widely spread in its distribution that only a 
very few of its most interesting localities can be referred to in this place. 

The finest specimens of rock crystals come from Dauphine, France; 
Carrara, in Tuscany, the Piedmont district, in Italy, and in the United 
States from Middleville, and Little Falls, N. Y.; the Hot Springs, 
Ark v and from several places in Alexander Co., N. C. Smoky quartz 
is found in good crystals in Scotland, at Pans, Me.; in Alexander 



166 DESCRIPTIVE MINERALOGY 

Co , N C , and in the Pike's Peak region of Colorado The handsomest 
amethysts come from Ceylon, Persia, Brazil, Nova Scotia and the 
country around Lake Superior Rose quartz occurs in large quantity 
at Hebron, Pans, Albany and Georgetown, Me 

Fine agates and carnehans are brought from Arabia, India and Brazil. 
They are abundant in the gravels of Agate Bay and of other bays and 
coves on the north shore of Lake Superior 

Chalcedony is abundant in the rocks of Iceland and the Faroe Islands, 
in those on the northwest side of Lake Supenor, and in the gravels of 
the Columbia, the Mississippi and other western rivers 

The other valuable varieties of the mineral occur largely in the Far 
East 

Agatized, or sihcified, wood of great beauty exists in enormous quan- 
tity in an old petrified forest near Cornzo, Ariz It is also found in 
the Yellowstone Park, near Florissant, Colo , and in other places in the 
Far West. This wood has had all of its organic matter replaced mole- 
cule for molecule by quartz in such a manner that its original structure 
has been perfectly preserved 

Uses Rock crystal is used more or less extensively m the construc- 
tion of optical instruments and in the manufacture of cheap jewelry 
Smoky quartz, amethyst, onyx, carnehan and heliotrope stones are 
used as gems, and agate, prase, chrysoprase and rose quartz as orna- 
mental stones 

Milky quartz, ground to coarse powder, is employed in the manu- 
facture of sandpaper. Its most extensive use, however, is in the man- 
ufacture of glass and pottery Earthenware, porcelain and some other 
varieties of potter's ware are vitrified mixtures of clay and ground 
quartz, technically known as "flint " Ordinary glass is a silicate of 
calcium or lead and the alkalies, sodium or potash It is made by 
melting together soda, potash, lime or lead oxide and ground quartz or 
quartz sand, and coloring with some metallic salt A pure quartz glass 
is now being made for chemical uses by melting pure quartz sand 

Quartz is sometimes used as a flux in smelting operations In the 
form of sandstone, it is used as a building stone, and in the form of sand 
it is employed in various building operations Bncks cut from dense 
quartzites (very hard and compact sandstones) are often employed 
for lining furnaces 

The uses of honestones, oilstones, and whetstones are indicated by 
their names. 

Production Many varieties of quartz are produced in the United 
Slates to serve various uses* Vein quartz is crushed and employed 



OXIDES 167 

in the manufacture of wood filler, paints, pottery, scouring soaps, sand- 
paper and abrasives It is also used in making ferro-silicon, chemical 
ware, pottery, sand-lime brick, quartz glass, etc The total quantity 
produced for these purposes in 1912 was 97,874 tons, valued at 
$191,685 

The largest quantity of quartz produced is in the form of sand, of 
which 38,600,000 tons were marketed in 1912 at a valuation of $15,300,- 
ooo Sandstone, valued at $6,900,000, was quamed for building and 
paving purposes Oilstones, grindstones, millstones, etc., which are 
made from special varieties of sandstone, were produced to the value of 
$1,220,000 

Gem quartz obtained in 1912 was valued at about $22,000. This 
comprised petrified wood, chrysoprase, agate, amethyst, rock crystal, 
smoky quartz, rose quartz, and gold quartz (white quartz containing 
particles of gold). 

THE METALLIC DIOXIDES 

The metallic dioxides include the oxides of tin, titanium, manganese 
and lead Of these the manganese dioxide may be dimorphous, and the 
titanium dioxide is-tnmorphous. A dioxide of zirconium is also* known, 
baddeleytfe, but it is extremely rare. The mineral zircon (ZrSiO4) is 
often regarded as being isomorphous with cassttente (Sn02) and rutile 
(Ti02) because of the similarity in the crystallization of the three min- 
erals The three, therefore, are placed in the same group, in which 
case all must be regarded as salts of metallic acids, thus: Ti0 2 =TiTiO4, 
SnO2=SnSn04, zircon =ZrSi04 Other authorities regard zircon as an 
isomorphous mixture of Ti02 and Si02. In this book zircon is placed 
with the silicates and the other minerals are considered as oxides. 

The two manganese dioxides are poliantfe and pyrolusite. The former 
is tetragonal and the latter orthorhombic It is possible, however, that 
the crystals of pyrolusite are pseudomorphs and that the substance is a 
mixture of poliamte and some hydroxide, as it nearly always contains 
about 2 per cent HgO. 

The three titanium oxides are ridde, which is tetragonal; brookitc, 
which is orthorhombic, and anatase or octakednte, which is tetragonal. 
Although rutile and anatase crystallize in the same system, their axial 
ratios are different, as are also their crystal habits and their physical 
properties. A few of these differences are indicated below: 

Rutde a:c=i: .6439; Sp. Gr. =4-283; = 2.6158; $= 2.9029. 
Anatase -1:1.7771; Sp. Gr. =3.9 ; ^=2.5618; ^=2.4886. 



168 DESCRIPTIVE MINERALOGY 

Of the tliree modifications of titanium dioxide, anatase may be 
made at a comparatively low temperature Brookite requires a higher 
temperature for its production, but rutilfc is producible at both high 
and low temperatures Under the conditions of nature both brookite 
and anatase pass readily into rutile 

Of the seven dioxides discussed, four are members of a single group 

RUTILE GROUP 

The rutile group consists of four minerals apparently completely 
isomorphous, though no mixed crystals of any two have been discovered : 
All crystallize in the tetragonal system (ditetragonal bipyramidal class), 
with the same forms and with closely corresponding axial ratios The 
names of the members of the group and their axial ratios follow 

Cassitente (Sn02) a c =i . 6726 

Ruttle (Ti0 2 ) =i 6439 

Pohamte (Mn02) =i ' 6647 

Plattnente (PbOa) =i ' 6764 

Cassiterite (Sn0 2 ) 

Cassiterite, or tinstone, is the only worked ore of tin It occurs as 
rolled pebbles of a dark brown color in the beds of streams, as fibrous 
aggregates, and as ghstemng black crystals associated with other min- 
erals in veins 

The analyses of cassitente indicate it to be essentially an oxide of 
tin, or, possibly, a stanyl stannale ((SnOJSnOa), with the composition, 
Sn=78.6 per cent; 0=2i 4 per cent. The mineral nearly always con- 
tains some iron oxide and often oxides of tantalum, of zinc or of arsenic 
The presence of iron and tantalum is so general that most crystals of 
cassitente may be regarded as isomorphous mixtures of (SnO)(SnOs) ; 
Fe(SnOs) and Fe(TaOs)2- Thus, a crystal from the Etta Mine in the 
Black Hills, S. D, gave Sn02=9436; FeO-i62, Ta 2 5 =242 and 
8102=100, indicating a mixture of 5 pts of Fe(TaOs)2, 18 pts. of 
Fe(SnOs) and 303 5 pts of (SnO)(SnOs). 

The crystals of cassitente have an axial ratio of i : ,6726. They are 
usually short prisms in habit They often consist of the simple com- 
bination P(in) and POO(IOI) (Fig 77), or of these forms, together 
with sPf (321) and various prisms (Fig 78). Twins are common, the 

1 An isomorphous mixture of the rutile and cassitente molecules has recently 
been described from Greifenstem, Austria, but its existence has not yet been con- 
firmed 



OXIDES 



169 



twinning plane being P oo (101) When the individuals twinned have 
small prismatic faces the resulting combination is often called a visor 
twin (Fig 79), because of its supposed resemblance to the vitor of a 
helmet By repetition of the twinning very complex groupings are 
produced The angle in A * ^* 58 19' 





FIG 77 FIG 78 

FIG. 77. Cassitente Crystal with P, m (s) and P * , 101 fc) 
FIG 78. Cassitente Crystal with s, e and o P, no (m), o P2, 210 (A), 3pJ, 321 (=). 

The cleavage of cassitente is imperfect parallel to oo P oo (100) and 
P(III) Its fracture is uneven The color of the massive mineral is 
some dark shade of brown by reflected light, and of the crystals black 
By transmitted light, the mineral is brown or black Its luster is very 
brilliant, and its streak is white, gray or brown. The purest specimens 





FIG 79 Cassitente Twinned about P 5 (101), o=ooPoo,ioo A=*VisorTwin. 

are nearly transparent, though the ordinary varieties are opaque Their 
hardness is about 6 5 and density about 7 The mineral is a noncon- 
ductor of electricity Its refractive indices for yellow light are: w = 1 9965, 
6=2.0931. 

Three varieties of cassitente are recognized, distinguished by physical 
characteristics The ordinary variety known as tinskme is crystallised 



170 DESCRIPTIVE MINERALOGY 

or massive. Wood tin is a botryoidal or remform variety, concentric in 
structure and composed of radiating fibers The third variety is stream 
tin This consists of water-worn pebbles found m the beds of streams 
that flow over cassitente-bearmg rocks 

Cassitente is only slightly acted upon by acids It may be reduced 
to a metallic globule of tin only with difficulty, even when mixed 
with sodium carbonate and heated intensely on charcoal. With 
borax it yields slight reactions for iron, manganese or other impurities 
When placed in dilute hydrochloric acid with pieces of granulated zinc, 
fragments of cassiterite become covered with a dull gray coating of 
metallic tin which can be burnished by rubbing with a doth or the hand 
When rubbed by the hand the odor of tin in contact with flesh is easily 
detected. 

The mineral is most easily distinguished from other compounds that 
resemble it in appearance by its high density and its inertness when 
treated with reagents or before the blowpipe 

Syntheses Crystals of cassiterite have been obtained by passing 
steam and vapor of tin chloride or tin fluoride through red-hot porcelain 
tubes, and by the action of tin chloride \apor upon lime 

Occurrence and Origin. Tinstone is found as a primary mineral in 
coarse granite veins with topaz, tourmaline, fluorite, apatite and a great 
number of other minerals It also occurs impregnating rocks, sometimes 
replacing the minerals of which they originally consisted. In these 
cases it is the product of pneumatolytic processes. In many places it 
constitutes a large proportion of the gravel in the beds of streams 

Localities and Production The crystallized mineral occurs at many 
places in Bohemia and in Saxony, at Limoges in France and sparingly 
in a few places in the United States, especially near El Paso, Texas, 
in Cherokee Co., N. C , in Lincoln Co , S C , and near Hill City, S D 
Massive tinstone and stream tin occur in laige enough quantities to be 
mined in Cornwall, England, on the Malay Peninsula and on the islands 
lying off its extremity; in Tasmania; in New South Wales, Victoria 
and Queensland, Australia; in the gold regions of Bolivia, at Durango 
in Mexico, and at various points in Alaska, at some of which there, 
are 400 Ib. of cassiterite in a cubic yard of gravel. 

The principal tin ore-producing regions of the world are the Straits, 
district, including the Malay Peninsula and the islands of the Malay 
Archipelago; Australia; Cornwall, England, the Dutch East Indies, and 
Bolivia* Of the total output of 122,752 tons of tin produced m 1911, 
61,712 tons were made from the Straits ore, 25,312 tons from the ore 
produced in Bolivia and 16,800 tons from Banka ore. Of the total 



OXIDES 



171 



quantity of tin produced about 78 per cent is said to come from stream 
tin and 22 per cent from ore obtained from veins. The quantity 
obtained from ore mined in the United States in igu included 61 tons 
from Alaskan stream tin and two tons from the tinstone mined in the 
Franklin Mountains near El Paso, Texas Mines have been opened in 
San Bernardino Co , California, and in the Black Hills, South Dakota, 
but they have not proved successful The mines at El Paso, Texas, are 
not yet fully developed, although they promise to be profitable in the 
near future The crystals are scattered through quartz veins and 
through a pink granite near the contacts with the veins The average 
composition of the ore is 2 per cent This is concentrated to a 60 per 
cent ore before being smelted The production during 1912 was 130 
tons of stream tin from Buck Creek, Alaska This was valued at 
$124,800. In the following year 3 tons of cassitente ^ere shipped from 
Gaffney, S C The imports of tin into the United States during 1911 
were 53,527 tons valued at more than $43,300,000 

Enaction The tin is extracted from the concentrated ore by the 
simple process of reduction Alternate layers of the ore and charcoal 
are heated together in a furnace, when the metal results This collects 
in the bottom of the furnace and is ladled or run out The crude metal is 
refined by remeltmg m special refining furnaces 

Uses of the Metal The metal tin is employed principally for coating 
other metals, either to prevent rusting or to pre\ent the action upon 
them of chemical reagents Tin plate is thin sheet iron covered with 
tin Copper for culinary purposes is also often co\ ered with this metal 
It is used also extensively in forming alloys with copper, antimony, 
bismuth and lead Among the most important of these alloys are 
bronze, bell metal, babbitt metal, gun metal, britanma, pewter and soft 
solder Its alloy, or amalgam, with mercury is used in coating mirrors. 
Several of its compounds also find uses m the arts Tin oside is an im- 
portant constituent of certain enamels The chlorides are used exten- 
sively in dyeing calicoes, and the bisulphide constitutes " bronze 
powder " or " mosaic gold," a powder employed for bronzing plaster, 
wood and metals 

Rutile (Ti0 2 ) 

Rutile is one of the oxides of the comparatively rare element titanium. 
It occurs commonly m dark brown opaque cleavable masses and in bril- 
liant black crystals 

Pure rutile consists of 40 per cent and 60 per cent TL Nearly all 
specimens, however, contain in addition some iron, occasionally as much 



172 



DESCRIPTIVE MINERALOGY 



as 9 per cent or 10 per cent, which is probably due to the admixture of 

and FeTiOs in solid solution 

Rutile is perfectly isomorphous with cassiterite Its axial ratio is 
i : 6439 The pnncipal planes observed on its crystals are practically 
the same as those observed on cassiterite (Fig 80) Twins aie common, 
with P oo (101) the twinning plane (Fig 81 ) This twinning is often 
repeated, producing elbow-shaped groups (Fig 82), or by further repe- 





FIG So. Rutile Crystals with o P, no (m), oo p oo , 100 (a), P oo , yoi (e), P, 111(5), 
>P3> 3io (0, p 3 313 (0 an d 3PJ, 321 00 





FIG 81 



FIG 82 



FIG 81 Rutile Eightling Twinned about P oo (101) 
FIG 82 Rutile Twinned about P oo (101) Elbow Twin 

tition wheel-shaped aggregates (Fig 83) In another common law the 
twinning plane is 3? oo (301") (Fig 84) The angle in A iTx 56 52^' 
The crystals are prismatic and even sometimes acicular in habit. Their 
prismatic planes are vertically striated 

The cleavage of rutile is quite distinct parallel to oo P(no) and less 
so parallel to oo P oo (100) 

The mineral is reddish brown, yellowish brown, black or bluish 
brown by leflected light and sometimes deep red by transmitted light, 
Many specimens are opaque but some are translucent to transparent. 



OXIDES 



173 



The latter are often pleochroic in tints varying between yellow and 
blood-red The streak is pale brown The hardness of the mineral is 
6 to 6 5 and its density about 42 It is an electric nonconductor at 
ordinary temperatures Its refractive indices for yellow light are: 
o>= 2 6030, =2 8894. 

Rutile is infusible and insoluble. Its reactions with beads of borax 
and microcosmic salt are usually obscured by the iron present When 
this metal is present only in small quantities the microcosmic salt bead 
is colorless while hot, but violet when cold, if it has been heated for some 
time in the reducing flame of the blowpipe 

The most characteristic chemical reaction of rutile is obtained upon 
fusing it with sodium carbonate on charcoal, dissolving the fused mass in 





FIG 83. FIG 84 

FIG 83 Rutile Cyclic Sixling Twinned about P (101) 

FIG 84 Rutile Twinned about 3? (301) Elbow Twin Forms P2, 210 (A), 

and P o , ioi (e) 

an excess of hydrochloric acid and adding to the solution small scraps of 
tin Upon heating for some little time, the solution assumes a violet 
color. This is a universal test for the metal titanium 

Some of the dark red and reddish brown massive varieties of rutile 
may be confounded with some varieties of garnet, which, however, are 
much harder. Its density, its infusibihty and the reaction for titanium 
serve to characterize the mineral perfectly 

Pseudomorphs of rutile after hematite and after brookite and ana- 
tase have been described It often changes into ilmenite and sphene. 

Syntheses. By the reaction between TiCU and water vapcr in a red- 
hot porcelain tube, crystals of rutile are formed. Twins are produced 
by submitting precipitated titanic acid in a mass of molten sodium tung- 
state to a temperature of 1000 for several weeks. 

Occurrence and Origin Rutile is often found as crystals embedded 
in limestone and m the quartz or f eldspar of granite and other igneous 



174 DESCRIPTIVE MINERALOGY 

rocks, as long acicular crystals m slates, and as grams in the rock known 
as nelsomte It occurs also as fine hair-like needles penetrating quartz, 
forming the ornamental stone " fleches d'amour," and as grains in the 
gold-bearing sand regions When primary it is probably always a 
product of magmatic processes, either crystallizing from a molten magma 
or being the result of pneumatolysis. 

Localities Handsome crystals of the mineral occur at Arendal, in 
Norway, in Tyrol, and at St Gothard and in the Binnenthal, Switzer- 
land In the United States large crystals have been obtained at Barre, 
Mass , at Sudbury, Chester Co , Penn ; at Stony Point, Alexander Co , 
N C , at Graves Mt , in Georgia, at Magnet Cove, in Arkansas, and 
in Nelson Co , Va. In the latter place it occurs in large quantity as 
crystals disseminated through a coarse granite rock The rock con- 
taining about 10 per cent of rutile is mined as an ore It constitutes the 
principal source of the mineral in the United States A second type 
of occurrence in the same locality is a dike-like rock, nelsomte, composed 
of ilmemte and apatite, in which the ilmemte is in places almost 
completely replaced by rutile 

Uses The mineral is not of great economic importance It is used 
in small quantity to impart a yellow color to porcelain and to give an 
ivory tint to artificial teeth. It is also used in the manufacture of the 
alloy ferro-titamum which is added to steel to increase its strength 
Recently the use of titamferous electrodes in arc lights, and the use of 
titanium for filaments in incandescent lamps ha\e been proposed Some 
of the salts of titanium are used as dyes and others as mordants Most 
of the ferro-titamum made m the United States is manufactured from 
titamferous magnetite 

Production The only rutile mined in the United States during 1913 
came from Roseland, Nelson Co., Virginia. It amounted to 305 tons of 
concentrates containing about 82 per cent TiOs At the same time there 
were separated about 250 tons of ilmemte (see p 462) 

Polianite (MnC^I is usually in groups of tiny parallel crystals and 
as crusts of crystals enveloping crystals of manganite (MnO OH). Their 
axial ratio is i ' 6647 The color of the mineral is iron-gray. Its streak 
is black, its hardness 6-6 5 and density 4 99. It dissolves in HC1 evolv- 
ing chlorine It is distinguished from pyrolusite by its greater hardness 
and its lack of water The mineral is extremely rare, being found in 
measurable crystals only at Platten in Bohemia It occurs in pseudo- 
morphs after manganite at a number of other points m Europe and at a 
few points elsewhere, but in most cases it has not been dearly distin- 



OXIDES 175 

guished from pyrolusite The rarity of its crystals is regarded by some 
mineralogists as being due to the fact that in most of its occurrences 
poliamte is colloidal (a gel) 

Plattnerite (PbO 2 ) is usually massive, but it occurs in prismatic 
crystals near Mullan in Idaho Their axial ratio is i : 6764 They are 
usually bounded by oo P oo (100), 3? oo (301), P oo (101), oP (ooi) and 
often IP (33 2) The mineral is found also in crusts Its color is 
iron-black and its streak chestnut-brown Its hardness is 5-5 5 and 
its density 86 It is brittle and is easily fusible before the blow- 
pipe, giving off oxygen and coloring the flame blue It yields a lead 
bead It is difficultly soluble in HNOs, but easily soluble in HC1 with 
evolution of chlorine. Plattnente is found at Leadhills and at Wanlock- 
head, Scotland, and at the " As You Like " Mine near Mullan, Idaho. 



Pyrolusite 

Pyrolusite is often the result of the alteration of the hydroxide, man- 
gamte, or of pohamte. The few measurable crystals that have been 
studied seem to indicate that their form is pseudomorphic after the 
hydroxide The change by which manganite may pass over into pyro- 
lusite is represented by the reaction 2MnO(OH)-f-0=2Mn02+H2O. 
Pyroiusite may be, however, only a slightly hydrated form of poliamte. 

An analysis of a specimen from Negaunee, Mich., gave 



MnO O CaO BaO SiOa Limomte HgO Total 

79 46 17 48 18 38 18 .31 i 94 99 93 

Pyrolusite, as usually found, is in granular or columnar masses, or in 
masses of radiating fibers It is a soft, black mineral with a hardness of 
only 2 or 2 5 and a density of about 4.8 Its luster is metallic and its 
streak black It is a fairly good conductor of electricity. 

The reactions of this mineral are practically the same as those of 
pohanite and manganite (see p 191), except that only a small quantity 
of water is obtained from it by heating. Upon strong heating it yields 
oxygen, according to the equation 3Mn02=Mn3+3Q2- 

The manganese minerals are easily distinguished from other minerals 
by the violet color they give to the borax bead and by the green prxjduct 
obtained when they are fused with sodium carbonate. Pyrolusite is 
distinguished from manganite by its physical properties, and from 
amte by its softness 



176 DESCRIPTIVE MINERALOGY 

Localities -Pyrolusite is worked at Elgersberg, near Ilmenau in 
Thuringia, at Vorder Ehrensdorf in Moravia, at Flatten in Bohemia, 
at CartersviUe, Ga , at Batesville, Ark , and m the Valley of Virginia 
A manganiferous silver ore containing considerable quantities of pyro- 
lusite is mined in the Leadville district, Colorado, and large quan- 
tities of manganiferous iron ores are obtained in the Lake Superior 
region 

Uses Pyrolusite, together with the other manganese ores with 
which it is mixed, is the source of nearly all the manganese compounds 
employed in the arts Some of the ores, moreover, are argentiferous 
and others contain zinc From these silver and zinc are extracted The 
most important use of the mineral is in the iron industry. In this indus- 
try, however, much of the manganese employed is obtained from man- 
gamferous iron ores The alloys spiegeleisen and ferro-manganese are 
employed very largely in the production of an iron used m casting car 
wheels. It is extremely hard and tough The manganese minerals are 
also used in glass factories to neutralize the green color imparted to glass 
by the ferruginous impurities m the sands from which the glass is made 
They are also used m giving black, brown and violet colors to pottery 
and some of their salts are valuable mordants Pyrolusite, finally, is the 
principal compound by the aid of which chlorine and oxygen are pro- 
duced. 

Production The United States in 1912 produced about 1,664 tons 
of manganese ores, valued at $15,723, and all came from Virginia, South 
Carolina and California In previous years the ores had been mined 
also m Arkansas, Tennessee and Utah Moreover, there were imported 
into the country 300,661 tons, valued at $1,769,000 Nearly all of this 
was used in the manufacture of spiegeleisen The domestic product was 
used in the chemical industries largely in the manufacture of manganese 
brick Of the manganiferous iron ores about 818,000 tons were produced 
ui 1912 These were utilized mainly as ores of iron, though a large por- 
tion was used as a flux. The product of manganiferous silver ores aggre- 
gated about 48,600 tons, all of which was used as a flux for silver-lead 
ores. Nearly all of this came from Colorado In addition there were 
imported iron-manganese alloys valued at $3,935,000. 



Anatase and BrooMte 

As has already been stated, the compound Ti02 is trimorphous, one 
form being orthorhombic and the two others tetragonal Of the latter, 
one has already been described as rutile The other is anatase, or octa- 
hednte. The orthorhombic form is known as brookite Anatase and 



OXIDES 177 

rutile are separated because of the difference in their axial ratios and in 
the habits of their crystals Both are ditetragonal bipyramidal, but 
a : c for rutile is i : 6439 and for anatase i . i 7771 Brookite is 
orthorhombic bipyramidal with a : b c- 8416 : i : .9444. 

Both anatase and brookite have the same empirical composition, 
which is similar to that of rutile 

Crystals of anatase are usually sharp pyramidal with the form P(in) 
predominating (Fig 85), blunt pyramidal with |P(ii3) or $P(ii7) 
predominating (Fig 86), or tabular parallel to oP(ooi) Twins are 
common in some localities, with P oo (101) the twinning plane. The 
angle in A iTi aBS 82 91' 

The mineral is colorless and transparent, or dark blue, yellow, brown 





FIG 86 

FIG 85 Anatase Crystal with P in (p) 

FIG 86 Anatase Crystal with fP, 113 (s), P, in (p), IP, 117 fr); P o (*), 
oo P oo , 100 (a) and P GO , 101 (t) 

or nearly black and almost opaque Its streak is colorless to light 
yellow. Its cleavage is perfect parallel to P and oP and its fracture 
conchoidal Its hardness is between 5 and 6 and its density is 3.9. This 
increases to 4 25 upon heating to a red heat, possibly due to its partial 
transformation into rutile The mineral is insoluble in acids except 
hot concentrated EkSO-i. It is a nonconductor of electricity. Its 
indices of refraction for yellow light are w= 2 5618, e= 2 4886 

Brooktte crystals are usually tabular parallel to oo P 60 (too) and 
elongated in the direction of the c axis Nearly all crystals are 
striated in the vertical zone Although many forms have been identi- 
fied on them, by far the most common is P2(i22) In some cases this is 
the only pyramidal form present, as in the type known as arkanstie 
(Fig. 87) Twins are rare, with oo 2(210) the twinning plane. The 
angle in AiTi ==: 64 17'. 



178 



DESCRIPTIVE MINERALOGY 



Brookite may be opaque, translucent or transparent Its color 
vanes from yellowish brown, through brownish red, to black (arkansite) 
Its streak is brownish yellow Its clea\age is imperfect parallel to 
oo Poo (101), and its fracture uneven or conchoidal Its hardness is 
5-6 and density about 4, Upon heating its density increases to that of 
rutile Its refractive indices for yellow light are a= 2 5832, #= 2 5856, 
7=2 7414 It fuses at about 1560, and is insoluble in acids 

The chemical properties of both brookite and anatase are similar 
to those of rutile They are distinguished from rutile by their physical 
properties and their crystallization 

Both brookite and anatase alter to rutile 

Syntheses Upon heating TiFi with water vapor at a temperature 





FIG 7 Brookite Crystals with coP, no (w), JP, 112 (z) and PsT, 122 (e) 
combination m and e is characteristic for \rkanbitc 



The 



below that of vaporizing cadmium, crystals of anatase are produced. 
If the temperature is raised above the point of vaporization of cadmium 
and kept below that of zinc, crystals of brookite result 

Occurrence Brookite and anatase occur as crystals on the walls of 
clefts in crystalline silicate rocks and in weathered phases of volcanic 
rocks. They are mainly pneumatolytic products, the production of the 
one or the other depending upon the temperature at which the TiCfe was 
deposited 

Localities Fine brookite crystals are found at St Gothard, in 
Switzerland, at Pregrattan, in the Tyrol, near Tremadoc, in Wales, 
at Miask, in Russia, and at Magnet Cove, Arkansas 

Anatase crystals are less common than those of brookite but they 
occur at many points in Switzerland, especially in the Binnenthal, 
near Bourg d'Oisans, France, at many points in the Urals, Russia, in 
the diamond fields of Brazil, and at the brookite occurrences m Arkansas, 



CHAPTER VIE 

* 

THE HYDROXIDES 

THE hydroxides, as has already been explained, may be looked upon 
as derivatives of water, m which only a portion of the hydrogen has been 
replaced. The group includes several minerals of economic importance, 
among which is the fine gem mineral opal All the hydroxides yield 
water when heated in a glass tube, but they do not yield it as readily as 
do salts containing water of crystallization 

A few of the hydroxides may act as acids forming salts with metals 
Diaspore, for instance, is an hydroxide of aluminium A10-OH, or 

/0-H 

Al< , which appears to be able to form salts, at least, the chemical 



composition of some of the members of an important group of minerals, 
the spinels, may be explained by regarding them as salts of this acid 
(seep 195) 

Opal (Si0 2 +Aq) 

The true position of opal in the classification of minerals is somewhat 
doubtful From the analyses made it appears to be a combination of 
amorphous silica and water, or, perhaps, a mixture of silica in some form 
and a hydroxide of silicon The percentage of water present is variable. 
In some specimens it is as low as 3 per cent, while in others it is as high 
as 13 per cent The mineral is not known in crystals. It is probably a 
colloid, in which the water is, in part at least, mechanically held in a gel 
of SiCfe. It occurs only m massive form, in stalactitic or globular masses 
and in an earthy condition. 

When pure the mineral is colorless and transparent Usually, how- 
ever, it is colored some shade of yellow, red, green or blue, when it is 
translucent or sometimes even opaque. The red and yellow varieties con- 
tain iron oxides and the green, prasopd, some nickd compound The 
play of color in gem opal is due to the interference of light rays reflected 
from the sides of thin layers of opal material with different densities 
from that of the mam mass of the mineral they traverse. The hardness 
of opal is 5 5-6 $ and its density about 2.1 Its refractive index for 
yellow light, n= 1.4401, It is a nonconductor of electricity. 

179 



180 DESCRIPTIVE MINERALOGY 

The principal varieties of opal are 

Precwus opal, a transparent variety exhibiting a delicate play of 
colors, 

Fire opal, a precious opal in which the colors are quite brilliant 
shades of red and yellow, 

Girasol, a bluish white translucent opal with reddish reflections, 

Common opal, a translucent variety without any distinct play of 
colors, 

Cachalong, an opaque bluish white, porcelain-like variety, 

Hyalite, a transparent, colorless variety, usually m globular or 
botryoidal masses, and 

Siliceous sinter, white, translucent to opaque pulverulent accumula- 
tions and hard crusts, deposited from the waters of geysers and other 
hot springs. 

Tnpolite and infusorial earth are pulverulent forms of silica in which 
opal is an important constituent Tripoli is a light porous siliceous 
rock, supposed to have resulted from the leaching of calcareous material 
from a siliceous limestone Infusorial earth represents the remains of 
certain aquatic forms of microscopic plants known as diatoms 

Flint and Chert are mixtures of opal, chalcedony and quartz 

All vaneties of opal are infusible and all become opaque when heated 
When boiled with caustic alkalies some varieties dissolve easily, while 
others dissolve very slowly. 

Syntheses Coatings of material like opal have been noted in glass 
flasks containing hydrofluosilicic acid that had not been opened for 
several years Opal has also been obtained by the slow cooling of a 
solution of silicic acid in water. 

Occurrence The mineral occurs as deposits around hot springs 
It also forms veins in volcanic rocks and is embedded in certain lime- 
stones and slates, where it is probably the result of the solution of the 
siliceous spicules and shells of low forms of Me and subsequent deposi- 
tion It also results from the solution of the calcite from limestones 
containing finely divided silica 

It is not an uncommon alteration product of silicates It seems to 
have been deposited from both cold and hot water 

Localities. Precious opal is found near Kashan, in Hungary, at 
Zimapan, Quaretaro, in Mexico, in Honduras, in Queensland and 
New South Wales, Australia, and in the Faroe Islands Common opal is 
abundant at most of these localities and is found also in Moravia, 
Bohemia, Iceland, Scotland and the Hebrides Hyalite occurs in small 
quantity at several places m New York, New Jersey, North Carolina, 



HYDROXIDES 181 

Georgia and Florida, and common opal, at Cornwall, Perm., and in 
Calaveras Co , California Common opal and vaneties exhibiting a little 
fire have recently been explored in Humboldt and Lander Counties, 
Nevada Siliceous sinter is deposited at the Steamboat Springs in 
Nevada and geysente (a globular form of the sinter) at the mouths of the 
geysers in the Yellowstone National Park 

Uses The precious and fire opals are popular and handsome gems 
Opahzed wood, i e , wood that has been changed into opal in such a 
manner as to retain its woody structure, is often cut and polished for use 
as an ornamental stone Infusorial earth, a white earthy deposit of 
microscopic shells consisting largely of opal material, possesses manv 
uses It is employed in the manufacture of soluble glass, polishing 
powders, cements, etc , and as the " body," which, saturated with nitro- 
glycerine, composes dynamite, Tripoli, a mixture of quartz and opal, 
is used as a wood filler, in making paint, as an abrasive and in the 
manufacture of filter stones. The principal sources of commercially 
valuable opal material in the United States are the opalized forest in 
Apache Co., Ariz , the infusorial earth beds at Pope's Creek and Dun- 
kirk, Md , various places in Napa Co , Cal , at Virginia City, Nev , 
and at Drakesville, N. J., and the tnpoh beds in the neighborhood of 
Stella, Mo , and the adjoining portion of Illinois 

Production The total quantity of infusonal earth and tnpoh mined 
during 1912 was valued at $125,446. The aggregate value of precious 
opal obtained in 1912 was $10,925. TluTcame from California and 
Arizona. 

Brucite (Mg(OH) 2 ) 

Brucite is the hydroxide of magnesium. It is a white, soft mineral 
usually occurring in crystals or in foliated masses 

Analyses of the mineral correspond very closely to the formula 
Mg(OH) 2 which requires 41 38 per cent Mg, 27 62 per cent and 31.00 
per cent EkO, though they usually show the presence of small quantities 
of iron and manganese A specimen from Reading, Perm., yielded: 

MgO F^O 3 MnO H 2 O Total 

67.64 82 63 3 92 I0 OI 

The crystallization of brucite is hexagonal (ditrigonal scalenohedral), 
a : c=i : 1.5208 The crystals are tabular in habit in consequence of 
the broad development of the basal plane oP(oooi). The other forms 
present are R(ioli), -^(0441) and -fRCoiTj) (Fig. 88) The angle 
roll A 7ioi = 97 38'. 




182 DESCRIPTIVE MINERALOGY 

The cleavage of brucite is very perfect parallel to oP(ooi), and folia 
that may be split off are flexible The mineral is sectiie Its hardness 
is 2 5 and its density 2 4 Its color is white, inclining to bluish and 
greenish tints, and its luster pearly on oP Brucite is transparent to 
translucent It is pyroelectnc and a non- 
conductor of electricity Its refractive indices 
for red light are i 559 == * 579 

In the closed tube brucite, like other hy- 
droxides, yields water The mineral is infusi- 
ble When intensely heated, it glows After 
FIG 88 Brucite Crystal heating, it reacts alkaline When moistened 
with oR, ocoi (<0, R, m fo cobalt mtrate solution and heated, it turns 

P mk the characterlstlc reaction for magnesium 
The pure mineral is soluble in acids 

Brucite resembles m many respects gypsum, talc, diaspore and some 
micas It is distinguished from diaspore and mica by its hardness and 
from talc by its solubility in acids Gypsum is a sulphate, hence the 
test for sulphur will sufficiently characterize it 

Synthesis Crystals have been made by precipitating a solution of 
magnesium chloride with an alcoholic solution of potash, dissolving the 
precipitate by heating with an excess of KOH and allowing to cool 

Occurrence and Origin Brucite is usually associated with other 
magnesium minerals It is often found in veins cutting the rock known 
as serpentine, where it is probably a weathering product, and is some- 
times found in masses in limestone, especially near its contact with 
igneous rocks 

Localities It occurs crystallized in one of the Shetland Islands, at 
the Tilly Foster Iron Mine, Brewster, N Y , at Woods Mine, Texas, 
Perm , and at Fritz Island, near Reading, in the same State 

Gibbsite (A1(OH) 3 ) 

Gibbsite, or hydrargillite, is utilized to some extent as an ore of alu- 
minium It occurs as crystals, in granular masses, in stalactites and in 
fibrous, radiating aggregates 

Its theoretical composition demands 6541 per cent AkOs and 
34.59 per cent H 2 Usually, however, the mineral is mixed with bauxite 
(AlsO(OH)4) and in addition contains also small quantities of iron, 
magnesium, silicon and often calcium 

Crystals are monodmic with a : b : 1=1.709 * i : i 918 and =85 
29!'. Their habit is tabular, Besides the basal plane, oP(ooi), the 



HYDROXIDES 183 

two most prominent forms are so Poo ( I00 ) anc j aop( IIO i Thus the 
plates have hexagonal outlines They ha\e a perfect cleavage parallel 
to the base Twinning is common, \\ith oP(ooi) the twinning plane 

The mineral has a glass} luster except on the basal plane where its 
luster is pearly It is transparent or translucent, Tvhite, pink, green or 
gray Its streak is light, its hardness is 2-3 and specific gravity 2 35 
It is a nonconductor of electricity. Its refractue indices are a =8 

= 15347, 7=15577 

When heated before the blowpipe the mineral exfoliates, becomes 
white, glows strongly but does not fuse Upon cooling the heated mass 
is hard enough to scratch glass The mineral dissolves slowly but com- 
pletely m hot HC1 and in strong HaSOi, and gives a blue color when 
moistened with Co(NOs)2 solution and heated. 

Gibbsite resembles most closely bauxite, from which it is distin- 
guished principally by its structure It differs from umelhte (p. 287), 
which it also sometimes resembles, in the absence of phosphorus. 

Syntheses Crystals of gibbsite have been made b\ heating on a 
water bath a saturated solution of Al(OH)s in dilute ammonia until all 
of the ammonia evaporates, and also by gradually precipitating the 
hjdroxide from a warm alkaline solution by means of a slow stream 
ofCO 2 

Occurrence The mineral rarely occurs in pure form It is found in 
veins and in cavities in various schistose and igneous rocks. It is prob- 
ably a weathering product of aluminous silicates. 

Localities Gibbsite has been reported as existing in small quantities 
at various points m Europe, near Bombay, India, and at several places 
in South America and Africa. In the United States it occurs at Rich- 
mond, Mass , at Union Vale, Dutchess Co , N Y., and mixed with 
bauxite at several of the occurrences of this mineral (see page 186). 

Uses. It is mined with bauxite as a source of aluminium. 

Limonite (Fe 4 O 3 (OH) b ) 

Limomte is an earthy or massrve reddish brown mineral whose 
composition and crystallization are but imperfectly known It is an 
important iron ore called in the trade " brown hematite " 

The analyses of limomte range between wide limits, largely because 
of the great quantities of impurities mixed with it. The formula de- 
mands 59 8 per cent Fe, 25 7 per cent and 14.5 per cent water, but the 
percentages of these constituents found in different specimens only 
approximately correspond to these figures Many mineralogists regard 



184 



DESCRIPTIVE MINERALOGY 




Fte 89 Limonite Stalactites in Silverbow Mine, Butte, Mont (After W H Weed ) 




Era 90 Botiyoidal Lunomte 



HYDROXIDES 185 

limomte as colloidal goethite (FeO OH > with one molecule or more of 
EfeO, depending upon temperature The principal impurities are clay, 
sand, phosphates, silica, manganese compounds and organic matter 
The great variety of these is thought to be due to the lact that the 
hmonite, like other gels, possesses the po\\er of absorbing compounds 
from their solution, so that the mineral is in reaht> a mixture of col- 
loidal iron h\ dro\ide and \ anous compounds which differ in different 
occurrences 

The mineral occurs in stalactites (Fig 8g\ in botiyoidd forms tFig 
90), in concretionary and clay-like masses and often as pseudomorphs 
after other minerals and after the roots, lea\es and stems of trees 

Limomte is brown on a fresh fracture, though the surface of mc.ny 
specimens is co\ ered \uth a black coating that is so lustrous as to appear 
varnished Its streak is yellowish brown Its hardness is a little o\ er 
5 and its density about 3.7. The mineral is opaque and its luster is dull, 
silky or almost metallic according to the ph\sical conditions of the spec- 
imen. Its index of refraction is about 25 It is a nonconductor of 
electricity 

The varieties recognized are. compact, the stdactitic and other 
fibrous forms, ocherous, the brown or yellow ecrthy, impure variety, 
bog iron^ the porous variety found in marshes, pseudomorphing leaves, 
etc , and brown clay ironstone, the compact, massive or nodular 
form. 

In its chemical properties limomte resembles goer tie, from ^hich it 
can be distinguished only with great difficulty except when the latter is 
in crystals From uncrystalhzed varieties of goethite it can usually be 
distinguished only by quantitative analysis, although in pure specimens 
the streaks are different 

Occurrence and Origin. Limonite is the usual result of the decom- 
position of other iron-bearing minerals Consequently, it is often found 
in pseudomorphs. In almost all cases 'ahere large beds of the ore occur 
the material has been deposited from ferriferous water nch in organic 
substances One of the commonest types of occurrence is " gossan." 
In the production of this type of ore, those portions of veins carrying 
ferruginous minerals are oxidized under the influence of oxygen-bearing 
waters, forming a layer composed largely of limonite which covers the 
upper portion of the veins and hides the original vein matter Gossan 
ores denved from chalcopynte and pynte are common in all regions in 
which these minerals occur Another type of limonitic ore comprises 
those found in clays derived from limestones by weathering In such 
deposits the ore occurs as nodules and in pockets in the day. Ores of 



186 DESCRIPTIVE MINERALOGY 

this type are common in the valleys within the Appalachian Moun- 
tains Bog iron ores occur in swamps and lakes into which ferruginous 
solutions drain The iron may come from pynte or iron silicates in the 
drainage basins of the lakes or swamps When carried down it is oxi- 
dized by the air and sinks to the bottom 

Localities The mineral occurs abundantly and in many different 
localities The most important American occurrences are extensive 
beds at Salisbury and Kent, Conn , at many points in New Jersey, 
Pennsylvania, Michigan, Tennessee, Alabama, Ohio, Virginia and 
Georgia 

Uses Although containing less iron than hematite, on account of 
its cheapness, and the ease with which it works in the furnace, brown 
hematite is an important ore of this metal The earthy \arieties are 
used as cheap paints 

Production The yield of the United States " brown hematite " 
mines for 1912 was a little over 1,600,000 tons Of this amount the 
largest yields were 

Alabama 749,242 tons 

Virginia 398,833 tons 

Tennessee 171,130 tons 

The quantity of ocher produced in the United States during the same 
year amounted to about 15,269 tons, valued at $149,289 Most of it 
came from Georgia In addition, 8,020 tons were imported. This 
had a value of $148,300 

Bauxite (A1 2 O(OH) 4 ) 

Bauxite, or beauxite, like hmomte, is probably a colloid At any 
rate it is unknown in crystals Until recently it possessed but little 
value It is now, however, of considerable, importance as it is the prin- 
cipal source of the aluminium on the market 

The mineral is apparently an hydroxide of aluminium with the for- 
mula Al20(OH)4 or Al 2 0s 2H20 m which 26 i per cent is water and 
73 9 per cent alumina (Al 2 0s), but it may be a colloidal mixture of the 
gibbsite and diaspore (p 190) molecules, or of various hydroxides, 
since its analyses vary within wide limits A sample of very pure 
material from Georgia gave on analysis 

A1 2 O 3 Fe 2 3 Si0 2 Ti0 2 H 2 O 

62 46 81 4 72 23 31 o^ 



HYDROXIDES 



1ST 



Bauxite occurs in concretionan grains (Fig 91*, m earthy, clay-like 
forms and massu e, usually in pockets or lenses in cia\ resulting from the 
weathering of limestones or of s\emte It is \\hite when pure, but as 
usually found is yellow, gra> , red or brown in color, is translucent to 
opaque and has a colorless or very light streak. Its densitx is 2 55 
and its hardness anywhere between i and 3 Its luster is dull. It is 
a nonconductor of electricity 

Before the blowpipe bauxite is infusible In the closed'tube it yields 




FEG. 91 Pisohtic Bauxite, from near Rock Run, Cherokee Co , Ala. 

water at a high temperature. Its powder when intensely heated with a 
few drops of cobalt nitrate solution turns blue. The mineral is with 
difficulty soluble in hydrochloric acid. 

Occurrence and Origin Bauxite in some cases may be a deposit from 
hot alkaline waters, but in Arkansas it is a residual ^eathenng product 
of the igneous rock, syenite. It occurs in beds associated with corundum, 
clay, gibbsite and other aluminium minerals. 

Localities. Large deposits of the ore occur at Baux, near Aries, 
France, near Lake Wochem, in Carniola, in Nassau; at Antrim, Ire- 
land, in a stretch of country between Jacksonville, Fla., and Carters- 



188 DESCRIPTIVE MINERALOGY 

ville, Ga , in Saline and Pulaski Counties, Ark , m Wilkinson Co , Ga , 
and near Chattanooga, Tenn 

Preparation The ore is mined by pick and shovel, crushed and 
washed It is then, in some cases, dried and broken into fine particles 
The fine dust is separated from the coarser material, and the latter, 
which comprises most of the ore, is heated to 400 This changes the 
iron compounds to magnetic oxide which is separated electro-mag- 
neticaJly The concentrate contains about 86 per cent of AfaOb This 
is then purified and dissolved in a molten flux, in some cases cryolite, 
and is subjected to electrolysis The quantity of aluminium made in the 
United States during 1912 was over 65,600,000 Ib , valued at about 
$17,000,000. The value of the aluminium salts produced was about 
$3,000,000. 

Uses Bauxite (or more properly the mixture of bauxite and gibbs- 
ite) is practically the only commercial ore of aluminium which, on 
account of its lightness and its freedom from tarnish on exposure, has 
become a very popular metal for use in various directions It is em- 
ployed in castings where light weight is desired and in the manufacture 
of ornaments and of plates for interior metallic decorations It is also 
employed in the steel industry, and, in the form of wire, for the trans- 
mission of electricity The mineral is also used in the manufacture of 
aluminium salts, in making alundum (artificial corundum), and bauxite 
brick for lining furnaces, and in the manufacture of paints and alloys. 

Production The bauxite mined in the United States during 1912 
amounted to about 159,865 tons valued at $768,932, the greater portion 
coming from Arkansas This is about two-thirds the value of the pro- 
duction of the entire world 

Psilomelane 

Psilomelane is probably a mixture of colloidal oxides and hydroxides 
of manganese in various proportions In most specimens there is a 
notable percentage of BaO or 20 present, and m others small quantities 
of lithium and thallium. The barium and potassium components are 
thought to have been absorbed from their solutions 

The substance occurs in globular, botryoidal, stalactitic, and massive 
forms exhibiting, in many instances, an obscure fibrous structure Its 
color is black or brownish black and its streak brownish black and 
glistening. Its hardness is 5 5-6 and specific gravity 4.2 

Psilomelane is infusible before the blowpipe, m some cases coloring 
the flame green (Ba) and in others violet (K). With fluxes it reacts for 



HYDROXIDES 189 

manganese. In the closed tube it yields water. It is soluble in HC1 
with evolution of chlorine 

It is distinguished from most other manganese oxides and hydroxides 
by its greater hardness. 

Occurrence Psilomelane occurs in veins associated with pyrolusite 
and other manganese compounds, as nodules in clay beds, and as coatings 
on many mangamferous minerals In all cases it is probably a product 
of weathering 

Locahties It is found in large quantity at Elgersburg in Thuringia; 
at Ilfeld, Harz, and at various places in Saxony. In the United States 
it occurs with pyrolusite and other ores of manganese at Brandon, Vt ; 
in the James River Valley, and the Blue Ridge region of Virginia; in 
northeastern Tennessee; at Cartersville, Georgia, at Batesville, Arkan- 
sas, and in a stretch of country about forty miles southeast of San 
Francisco, California. At many of these points it has been mined as an 
ore of manganese 

Wad 

Wad is a soft, earthy, black or dark brown aggregate of manganese 
compounds closely related to psilomelane 

It occurs in globular, botryoidal, stalactitic, flaky and porous 
masses, which, m some cases, are so light that they float on water. It 
also occurs in fairly compact layers and coats the surfaces of cracks, 
often forming branching stains, known as dendntes 

Wad contains more water than psilomelane, of which it appears 
often to be a decomposition product. More frequently it results from 
the weathering of manganiferous iron carbonate It is particularly 
abundant in the oxidized portions of veins containing manganese car- 
bonates and silicates 

Wad is easily distinguished from all other soft black minerals, except 
pyrolusite^ by the reaction for manganese, and from all other manganese 
compounds, except pyrolusite, by its softness From pyrolusite it is 
distinguished by its content of water. 

Localities It occurs in most of the localities at which other man- 
ganese compounds are found. 

DIASPORE GROUP 

The diaspore group comprises the hydroxides of aluminium, iron 
and manganese, possessing the general formula R'"O(OH). They are 
regarded as hydroxides in which one of the hydrogens in BfeO is replaced 
by the group R /7/ 0, thus: H O H, water, A10 H, diaspore These 



190 



DESCRIPTIVE MINERALOGY 



three compounds from a chemical viewpoint, may be looked upon as the 
acids whose salts comprise the spinel group of minerals, which includes 
among others the three important ore minerals magnetite, chromite and 
frankhnite Of the three members of the diaspore group the manganese 
and iron compounds are valuable ores All are orthorhombic, in the 
rhombic bipyramidal class. 

Diaspore (AIO(OH)) 

Diaspore is found in colorless or light colored crystals, in foliated 
masses and in stalactitic forms 

Its composition is theoretically 85 per cent AbOs and 15 per cent 




Fro 92 Diaspore Crystals oo P So , oio (fi) , oo Pj , 130 (s) , GO P, no (m), 
210 (A), PS5, on (e), ?2, 212 (s), ooPl, 120 (/), P<j, 150 (), 



HgO, though analyses show it to contain, in addition, usually, some iron 
and silicon A specimen from Pennsylvania yielded. 



A1 2 3 

8095 



H 2 

14 84 



Fe 2 0s 

3 12 



Si02 Total 
i 53 100 44 



Other specimens approach the theoretical composition very closely 

In crystallization the mineral is orthorhombic (rhombic bipyramidal 
class), with a b . c= 9372 . i : 6039 The crystals are usually pris- 
matic, though often tabular parallel to oo P 56 (oio) The principal 
planes observed on them are oo Poo (oio), a series of prisms as 
ooP(no), oo Pa (210), oP3(i3o), the dome PQ&(OII) and several 
pyramids (Fig. 92) The planes of the prismatic zone are often ver- 
tically striated The angle no A i Io-86 if 

The cleavage of diaspore is very distinct parallel to the brachy- 
pmacoid. Its fracture is conchoidal and the mineral is very brittle, 
Its hardness is about 6 5 and density 3 4 The luster of the mineral is 
vitreous, except on the cleavage surface, where it is pearly. Its color 



HYDROXIDES 191 

varies widely, though the tint is always light and the streak colorless 
The predominant shades are bluish white, grayish white, yellowish or 
greenish white The mineral is transparent or translucent It is a 
nonconductor of electricity Its refractive indices for yellow light are 
a= 1702, j8=i 722, 7 = 1 750 

In the closed tube diaspore decrepitates and gives off water at a high 
temperature It is infusible and insoluble in acids. When moistened 
with a solution of cobalt nitrate and heated it turns blue, as do all other 
colorless aluminium compounds 

In appearance, diaspore closely resembles Irucite (Mg(OH)s), from 
which it may be distinguished by its greater hardness and its aluminium 
reaction with cobalt nitrate 

Synthesis Crystal plates of diaspore have been made by heating at 
a temperature of less than 500, an excess of amorphous AfeQs in sodium 
hydroxide, enclosed in a steel tube At a higher temperature corundum 
resulted. 

Occurrence Diaspore occurs as crystals implanted on corundum 
and other minerals, and on the walls of rocks in which corundum is 
found It is probably in most cases a decomposition product of other 
aluminium compounds 

Localities In Ekaterinburg, Russia, it is associated with emery. 
At Schemnitz, Hungary, it occurs in veins It is found also in the 
Canton of Tessin, in Switzerland, at various places in Asia Minor, and 
on the emery-bearing islands of the Grecian Archipelago. In the 
United States it is associated with corundum, at Newlin, Chester Co , 
Penn , with emery at Chester, Mass , at the Culsagee corundum mine, 
near Franklin, N C , and at other corundum mines in the same State. 

Manganite (MnO(OH)) 

Manganite usually occurs in groups of black columnar or prismatic 
crystals and in stalactites. 

The formula MnO(OH) requires 27 3 per cent 0, 62 4 per cent Mn 
and 10 3 per cent water, or 89 7 per cent MnO and 10 3 per cent water. 
In addition to these constituents, the mineral commonly contains also 
some iron, magnesium, calcium and often traces of other metals. An 
analysis of a specimen from Langban, in Sweden, yielded: 

Mn 2 O 3 Fe 2 3 MgO CaO H 2 O Total 
88 51 23 i 51 62 9 80 100 67 

The orthorhombic crystals of the mineral have an axial ratio a : i : c 
= 8441 : i : ,5448 The crystals are nearly all columnar with a series 



192 



DESCRIPTIVE MINERALOGY 



of pnsms, among which are oo P^io) and oo P(uo), and the two lateral 
pinacoids oo P 06 (oio) and 8 P a (100) terminated by oP(ooi) or by 
the domes P 06 (on), P 06 (101), and pyramids (Figs 93 and 94) Cru- 
ciform and contact twins, with the twinning plane P oo (on), are not 
uncommon (Fig 95) The prismatic surfaces are 
vertically striated and the crystals are often in 
bundles The angle no A iTo=8o 20' 

Cleavage is well defined parallel to oo P 06 (oio) 
and less perfectly developed parallel to ooP(no) 
The fracture is uneven The luster of the mineral 
is brilliant, almost metallic Its color is iron-black 
and its streak reddish brown or nearly black It 
is usually opaque but in very thin splinters it is 
sometimes brown by transmitted light. Its hard- 
ness is 4 and density about 4 3. The mineral is 
a nonconductor of electricity 
Mangamte yields water in the closed tube and colors the borax bead 
amethyst m the oxidizing flame of the blowpipe. In the reducing flame, 
upon long-continued heating, this color disappears The mineral dis- 
solves in hydrochloric acid with the evolution of chlorine. It is dis- 




FIG 93 Mangamte 
Crystal with ooP, 
no(w), oP,ooi (c) 
and P 55 , ioi () 




FIG 94 Group of Prismatic Mangamte Crystals from Lfeld, Hare. 

tinguished from other manganese minerals by its hardness and crystal- 
lization. 

By loss of water mangamte passes readily into pyrolusite (MnCfe). 
It also readily alters into other manganese compounds 

Synthesis. Upon heating for six months a mixture of manganese 
chloride and damn caarbonate fine crystals like those of mangamte 




HYDROXIDES 193 

have been obtained Their composition, howe\er, was that of haus- 
manmte, indicating that \\hile mangamte was produced, it was changed 
to hausmanmte during the process. 

Occurrence, Localities and Origin Man- 
gamte occurs in veins in old volcanic rocks, 
and also in limestone It is found at Ilfeld 
in the Harz, at Ilmenau in Thurmgia, and 
at Langban in Sweden, in handsome cns- 
tals In the United States it occurs at the 
Jackson and the Lucie iron mines, Xegaunee, 

Mich , and in Douglas Co , Colo It is _ 

, , , . A : FIG 05 Manoamte Crvstal 

also abundant at ^arlous places m New Tvvmned ab j ut P ^ ( ' QII ^ 

Brunswick and Nova Scotia In all cases The torms are =c P notmj, 
it is a residual product of the weathering of =cP3,i2o./;andP3 31315) 
manganese compounds. 

Uses Mangamte is used in the production of manganese compounds. 
As mined it is usually mixed with pyrolusite, this being the most im- 
portant portion of the mixture 

Goethite (FeO(OH)) 

This mineral, though occasional!}- found m blackish brown crystals, 
usually occurs in radiated globular and botryoidal masses Analyses 
of specimens from Maryland, and from Lostwithiel, in Cornwall, gave- 

Fe 2 0s Mn 2 Q3 H 2 O SiCb Total 

Maryland 86 32 10 So 2 88 too oo 

Lostwithiel 89 55 16 10 07 28 100 06 

The formula FeO(OH) demands 89.9 per cent Fe2Qs and 10 i per cent 
H2O or 62.9 per cent Fe, 27 o per cent and 10 i per cent HaO 

Like diaspore and mangamte, goethite is orthorhornbic, its axial 
ratio being a : b : c = 9185 : i : .6068 Its crystals are prismatic or 
acicular with the prisms plainly striated vertically The forms observed 
are commonly oo P 06 (oio), QO PS(2io\ oo P(no), P 06 (on) and P(rii). 
The angle no A 1*10=85 8'. 

The deavage of goethite is perfect parallel to oo P 06 (oio) and its 
fracture uneven Its hardness is 5 and density about 4.4. Its color is 
usually yellowish, reddish or blackish brown and its luster almost 
metallic In thin splinters it is often translucent with a blood-red color 
and a refractive index of about 2 5 Its streak is brownish yellow. It 
is an electric nonconductor. 



194 DESCRIPTIVE MINERALOGY 

The chemical reactions of the mineral are about the same as those of 
hematite, except that it yields water when heated in the closed tube 
By this reaction it is easily distinguished from the fibrous varieties of 
hematite, as it is also by its streak 

Synthesis Needles of goethite are produced by heating freshly 
precipitated iron hydroxide for a long time at 100 

Occurrence and Localities Goethite is usually associated with other 
ores of iron, especially in the upper portion of veins, -where it is produced 
by weathering. It is found near Siegen in Nassau, near Bristol and 
Clifton, England, and in large, fine crystals at Lostwithiel and other 
places in Cornwall 

In the United States it occurs in small quantity at the Jackson and 
the Lucie hematite mines in Negaunee, Mich , at Salisbury, Conn , 
at Easton, Penn , and at many other places 

Uses Goethite is used as an ore of iron, but in the trade it is classed 
with limomte as brown hematite 



CHAPTER DC 
THE ALU3IIXATES, FERRITES, CHROMITES \XD MAXG \XITES 



MOST of these compounds are salts of the comparative!} uncommon 
acids HA1O2, HFeOo and HCrCb, \\hich may be regarded as metaacids 
derived from the corresponding normal acids by the abstraction of water, 
thus. HsAlOs H2O=HAlOo There are onh a few minerals belong- 
ing to the group but they are important One, magnetite, is an ore of 
iron, another, chronute, is the principal ore of chromium and two others 
are utilized as gems Most of them are included in the mineral group 
known as the spmels (Compare p 189 ) 

That there is a manganese acid corresponding to the metaacids of AI, 
Fe and Cr is indicated by the fact that in some of the spinels manganese 
replaces some of the fernc iron, as, for example, in frankhmte. This 
suggests that this mineral is an isomorphous mixture of a metafernte 
and a salt of the corresponding manganese acid (HMnCb) This may 
be regarded as derived from the hydroxide, MnfOH)s, by abstraction 
of H 2 O, thus- H 3 Mn03-H 2 CMHMnO.>. But there are other man- 
ganous acids Normal manganous acid is MnfOH)^, or H4Mn(>4 If 
from this one molecule of water be abstracted, there remains H2^InOs, 
the metamanganous acid The manganous salt of the normal acid, 
Mn2MnQi, occurs as the mineral, hausmannite, and the corresponding 
salt of the metaacid, MnMnOs, as the mineral, braunite. 

SPINEL GROUP 

The spinels are a group of isomorphous compounds that may be 
regarded as salts of the acids AIO(OH), MnO(OH), CrO(OH) and 
FeO(OH), in which the hydrogen is replaced by Mg, Fe and Cr. 

Al CX 
Thus, spinel, Mg- AfeQ* may be regarded as || yMg, magnetite, 

Fe Ov Cr O-Ov 

Fe 3 O 4 , as II >Fe; clromite, FeCx&O*, as || )>Fe, and 

Fe-O-(X Cr-O-CK 

(Fe Mn)-O-<X 

frankhmte, as I I y>(Zn-Mn Fe). Chemical compounds of 

(Fe Mn)-0-CK 

195 



196 



DESCRIPTIVE MINERALOGY 



this general type are fairly numerous, but only a few occur as minerals 
The most important are the three important ores mentioned above, 
spinel is of some value as a gem btone 

The spinels crystallize in the holohedral divi- 
sion of the isometric system (hexoctahedral class), 
in well defined crystals that are usually combina- 
tions of 0(ui) and ooO(no), with the addition on 
some of ooQoo (100), 303(311), 202(211), 50^(531), 
etc Contact twins are so common with the 
twinning plane, that this type of twinning is often 
referred to as the spinel twinning (Fig 96). 




FIG 96 

Spinel Twin 



The complete list of the known spinels is as follows. 



Spinel 

Ceylomte (pleonaste) 

CJdorspinel 

Picotite 

Hercynite 

Gahmte 

Dysluite 

Krwttomte 

Magnetite 

Magnesiofernte 

Frankhmte 

Jacobsite 

Chromite 



Mg(A10 2 ) 2 

(Mg Fe)(A10 2 ) 2 

Mg((Al Fe)0 2 ) 2 

(Mg Fe)((Al Fe-Cr)0 2 ) 2 

Fe(A10 2 ) 2 

Zn(A10 2 ) 2 

(Zn Fe Mn)((Al Fe)0 2 ) 2 

(Zn Fe Mg) ((Al Fe)O 2 ) 2 

Fe(Fe0 2 ) 2 

Mg(Fe0 2 ) 2 

(Fe ZnMn)((Fe Mn)O 2 ) 2 

(Mn Mg)((Fe Mn)0 2 ) 2 

(Fe Mg)(Cr Fe)0 2 ) 2 



Spinel (Mg(AlO 2 ) 2 ) 

Ordinary spinel is the magnesian alummate, which, when pure, con- 
tains 28 3 per cent MgO and 71 7 per cent 
AfeOa Usually, however, there are present 
admixtures of the other isomorphs so that 
analyses often indicate Fe, Al and Cr 

The mineral usually occurs in isolated 
simple crystals, rarely in groups The forms 
observed on them are 0(m), ooO(no) and 
303(311), and rarely oo oo (100) (Fig 97) 

The pure magnesium spinel is colorless or FlG 97 Spinel Crystal 
some shade of pink or red, brown or blue, and J^'Q ( ^r)" 
is usually transparent or translucent, though an 3 3 ' 3I1 
opaque varieties are not rare Its streak is white It possesses a glassy 




ALUMINATES, FERRITES, ETC 197 

luster, and a conchoidal fracture, but no distinct cleavage Its hard- 
ness is 8 and its density 3 5-3 6 Its refractive indices \ary with the 
color n for yellow light is i 7150 for red spinel and i 7201 for the blue 
variety. 

The mineral is infusible before the blowpipe and is unattacked by 
acids It yields the test for magnesia with cobalt solution 

Spinel is easily distinguished from most other minerals by its cns- 
tallization and hardness It is distinguished from pale-colored garnet 
by its blowpipe reactions, especially its infusibility, and its failure to 
respond to the test for Si02 

The best known varieties are: 

Precious spinel, which is the pure magnesian aluminate. It is trans- 
parent and colorless or some light shade of red, blue or green. The 
bright red variety is known as ruby spinel and is used as a gem Its 
color is believed to be due to the presence of chromium oxide It is 
easily distinguished from genuine ruby by the fact that it is not doubly 
refracting and not pleochroic. 

The best ruby spinels come from Ceylon, where they occur loose in 
sand associated with zircon, sapphire, garnet, etc. 

Common spinel differs from precious spinel m that it is translucent. 
It usually contains traces of iron and alumina. 

Both these varieties of spinel occur in metamorphosed limestones 
and crystalline schists. 

Syntheses The spinels have been made by heating a mixture of 
AkOs and MgO with boracic acid until fusion ensues, and by heating 
Mg(OH)2 with AlCls in the presence of water vapor 

Origin Spinel has been described as an alteration product of corun- 
dum and garnet It is also a primary component of igneous rocks and 
a product of metamorphism in rocks nch in magnesium 

Uses Only the transparent ruby spinels have found a use. These 
are employed as gems 

Ceylonite, or pleonaste, is a spinel in which a portion of the Mg 
has been replaced by Fe, i e , is an isomorphous mixture of the magne- 
sian and iron aluminates, thus ((Mg Fe)(AlO2)2) It is usually black 
or green and translucent, and has a brownish or dark greenish streak 
and a density =3 5-3 6 

The analysis of a sample separated from an igneous rock in Madison 
Co , Mont., gave, 



A1 2 O 3 FeO MgO CraOs Fe^ MnO CaO SiOa Total 
62 09 17 56 15 61 2 62 2 10 tr 16 55 100 69 



198 DESCRIPTIVE MINERALOGY 

Ceylomte occurs in igneous rocks m the Lake Laach region, 
Germany, and m the Piedmont district, Italy and elsewhere, m meta- 
morphosed limestones at Warwick and Amity, N Y , m the limestone 
blocks enclosed in the lava of Vesuvius, and m dolomite metamor- 
phosed by contact action at Monzoni, Tyrol 

Picotite, or chrome spinel, is a \anety intermediate between spinel 
proper and chromite Its composition may be represented by the 
formula (Mg Fe)((Al Fe Cr)O2)2 It occurs only m small crystals in 
basic igneous rocks and in a few crystalline schists Density =4 i 

Magnetite (Fe(FeO 2 ) 2 ) 

Magnetite, the ferrous fernte, the empirical formula of which is 
FesO-i, is a heavy, black, magnetic mineral which is utilized as one of 
the ores of iron 

The pure mineral consists of 72 4 per cent Fe and 27 6 per cent 
Most specimens, however, contain also some Mg and many contain small 
quantities of Mn or Ti A selected sample of magnetite from the Eliza- 
beth Mine, Mt Hope, New Jersey, analyzed as follows 

Fe 2 O 3 FeO Si0 2 Ti0 2 A1 2 3 MgO CaO Other Total 
65 26 30 20 i 38 i 09 55 10 68 73 99 99 

Magnetite occurs in crystals that are usually octahedrons or dodeca- 
hedrons, or combinations of the two , Other forms are rare Twins 
are common The mineral occurs also as sand 
and in granular and structureless masses When 
the dodecahedron is present, its faces are fre- 
quently striated parallel to the edge between 
ooO(no) and 0(ui) (Fig 98) 

Magnetite is black and opaque and its streak FIG 98 Magnetite 
is black It has an uneven or a conchoidal f rac- Crystal, with w o 
ture, but no distinct cleavage Its hardness is (llo) and (l3CI ) 
S.S^andd eM1 ty49-5* It is strongly attracted f* 
by a magnet and in many instances it exhibics and in 
polar magnetism 

The mineral is infusible before the blowpipe Its powder dissolves 
slowly in HC1, and the solution reacts for ferrous and ferric iron 

Magnetite is easily recognized by its color, magnetism, and hardness 

The mineral weathers to lunomte and hematite and occasionally to 
the carbonate, sidente, 




ALUMINATES, FERRITES, ETC. 199 

Syntheses. Crystals have been made by cooling iron-bearing silicate 
solutions, treating heated ferric hydroxide \\ith HC1, and by fusing 
iron oxide and borax with a reducing flame 

Occurrence end Ongm. The mineral occurs as a constituent of 
many igneous rocks and crystalline schists, and in lenses embedded in 
rocks of many kinds It also constitutes veins cutting these rocks 
and as irregular masses produced b\ the deh\ dration and deoxidation 
of hematite and limomte under the influence of metamorphic processes. 
It occurs also as little grains among the decomposition products of 
iron-bearing silicates, such as olmne and hornblende. 

The larger masses are either segregations from igneous magmas or 
deposits from hot solutions and gases emanating from them. 

Localities The localities at \\hich magnetite has been found are so 
numerous that only those of the greatest economic importance may be 
mentioned here. In Norway and Sweden great segregated deposits are 
\\orked as the principal sources of iron in these countries. In the 
United States large lenses occur in the limestones and siliceous crys- 
talline schists in the Adirondacks, New York, and in the schists and 
granitic rocks of the Highlands in New Jersey Great bodies are mined 
also at Cornwall, and smaller bodies at Cranberry, and in the Far 
West 

Extraction The magnetite is separated from the rock with which it 
occurs by crushing and exposing to the action of an electro-magnet. 

Production The total amount of the mineral mined m the United 
States during 1912 was 2,179,500 tons, of which 1,110,345 tons came 
from New York, 476,153 tons from Pennsylvania, and 364,673 tons 
from New Jersey. 

FrankEnite ((Fe-Zn Ua)((Fe-Hn)O 2 ) 2 ) 

Franklinite resembles magnetite in its general appearance. It is an 
ore of manganese and zinc 

It differs from magnetite m containing Mn in place of some of the 
ferric iron in this mineral and Mn and Zn in place of some of its ferrous 
iron. Since it is an isomorphous mixture of the iron, zinc and manganese 
salts of the iron and manganese acids of the general formula R"'0(OH), 
its composition varies within wide limits The franklinite from Mine 
Hill, N. J , contains from 39 per cent to 47 per cent Fe, 10 per cent to 
19 per cent Mn and 6 per cent to 18 per cent Zn A specimen from 
Franklin Furnace, N J., contained, 

Fe 2 03 MnO ZnO MgO CaO SiOa HsO Total 
66 58 9 96 so 77 34 -43 -7 2 -7 1 99-5* 



200 DESCRIPTIVE MINERALOGY 

Its crystals are usually octahedrons, sometimes modified by the do- 
decahedron and occasionally by other forms The mineral occurs also 
in rounded grams, in granular and in structureless masses 

It is black and lustrous and has a dark brown streak Its fracture 
and cleavage are the same as for magnetite It is only very slightly 
magnetic It has a hardness of 6 and a density of 5 15 

The mineral is infusible before the blowpipe When heated on 
charcoal it becomes magnetic When fused with Na2COa in the oxidizing 
flame it gives the bluish green bead characteristic of manganese Its 
fine powder mixed with Na2COa and heated on charcoal yields the white 
coating of zinc oxide which turns green when moistened with Co(N03)2 
solution and again heated 

Franklinite is distinguished from most minerals by its color and crys- 
tallization and from magnetite and clromite by its brown streak and 
by its reactions for Mn and Zn It is also characterized by its associa- 
tion with red zmcite and green or pink willemite (p 306) 

Synthesis Crystals of franklmite have been made by heating a 
mixture of FeCla, ZnCb and CaO (lime) 

Occurrence and Origin Franklimte occurs at only a few places Its 
most noted localities are Franklin Furnace and Sterling Hill, N J , where 
it is associated in a white crystalline limestone with zmcite, willemite 
and other zinc and manganese compounds The deposit is supposed 
to have been produced by the replacement of the limestone through the 
action of magmatic waters and vapors. 

Uses. The mineral is utilized as an ore of manganese and zinc 
The ore as mined is crushed and separated into parts, one of which 
consists largely of franklmite This is roasted with coal, when the zinc 
is driven off as zinc oxide The residue is smelted in a furnace producing 
spiegeleisen, which is an alloy of iron and manganese used in the man- 
ufacture of certain grades of steel 

Production The quantity of this residuum produced in 1912 was 
104,670 tons, valued at $314,010 

Chromite (Fe(CrO2)2) 

Chromite, or chrome-iron, is the principal ore of chromium. It 
resembles magnetite and frankhnite in appearance It occurs in iso- 
lated crystals, in granular aggregates, and in structureless masses. 

Chemically, it is a ferrous salt of metachromous acid, of the theoret- 
ical composition Cr20a=68 per cent and FeO=32 per cent, but it usually 
contains also small quantities of Al^Oa, CaO and MgO An analysis of 



ALUMINATES, FERRITES, ETC 201 

a specimen from Chorro Creek, California, after making corrections for 
the presence of some serpentine, yielded 

Cr 2 3 A1 2 3 Fe 2 3 FeO MgO MnO Total 

56 96 12 32 3 81 12 73 14 02 16 100 oo 

Its crystals are usually simple octahedrons, but they are not as 
common as those of the other spinels 

Its color is brownish black and its streak brown It has a conchoidal 
or uneven fracture and no distinct clea\age It is usually nonmag- 
netic, but some specimens sho\\ slight magnetism because of the ad- 
mixture of the isomorphous magnetite molecule Its hardness is 5 5 
and its density 4 5 to 4 8 

The mineral is infusible before the blowpipe It gives the chromium 
reaction with the beads If its powder is fused with niter and the fusion 
treated with water, a yellow solution of KoCrO4 results When fused 
with NagCOs on charcoal it yields a magnetic residue. 

Chromite is easily distinguished from all other minerals but ptco- 
tite by its crystallization and its reaction for chromium. It is distin- 
guished from picotite by its inferior hardness and its higher specific 
gravity. 

Synthesis Crystals have been made by fusing the proper constit- 
uents with boric acid and after fusion distilling off the boric acid. 

Occurrence and Origin Chromite occurs principally in olivine rocks 
and in their alteration product serpentine The mineral is found not 
only as crystals embedded in the rock mass, but also as nodules in it 
and as veins traversing it It is probably in all cases a segregation from 
the magma producing the rock In a few places the mineral occurs 
in the form of sand on beaches 

Localities It is widely spread through serpentine rocks at many 
places, notably in Brussa, Asia Minor; at Banat and elsewhere in 
Norway; at Solnkive, in Rhodesia, in the northern portion of New 
Caledonia, at various points in Macedonia, in the Urals, Russia; in 
Beluchistan and Mysore, India 

In the United States the mineral is known at several points in a belt 
of serpentine on the east side of the Appalachian Mountains, and at 
many points in the Rocky Mountains, the Sierra Nevada and the Coast 
Ranges It has been mined at Bare Hills, Maryland, in Siskiyou, 
Tehama and Shasta Counties, Colorado, in Converse County, Wyoming; 
and in Chester and Delaware Counties, Pennsylvania, and in 1914, 
some was washed from chrome sand at Baltimore, Maryland. 



202 DESCRIPTIVE MINERALOGY 

Metallurgy The mineral is mined by the usual methods and con- 
centrated, or, if in large fragments, is crushed It is then fused with 
certain oxidizing chemicals and the soluble chromates are produced. 
Or the ore is reduced with carbon yielding an alloy with iron The 
metal is produced by reduction of its oxide by metallic aluminium or by 
electrolysis of its salts 

jj ses Chromite is the sole source of the metal chromium, which is 
the chrome-iron alloy employed m the manufacture of special grades 
of steel Chromium salts are used in tanning and as pigments The 
crude ore, mixed with coal-tar, kaolin, bauxite, or some other ingredient, 
is molded into bricks and burned, after which the bricks are used as 
linings in metallurgical furnaces. These bricks stand rapid changes of 
temperature and are not attacked by molten metals 

Production The annual production of chromite in the world is 
now about 100,000 tons, of which Rhodesia produces about J, New 
Caledonia about | and Russia and Turkey about \ each The produc- 
tion of the United States in 1912 was 201 tons, valued at $2,753. All 
came from California. The imports in the same year were 53,929 tons, 
worth $499,818. 



Chiysoberyl 

Chrysoberyl is a beryllium alummate, the composition of which is 
analogous to that of the spinels It may be written Be02(A10)2. Al- 
though theoretically it should contain 19 8 per cent BeO and 80 2 per 
cent AkOa, analyses of nearly all specimens show the presence also of 
iron and magnesium 

The mineral differs from spinel in crystallizing in the orthorhombic 
system (bipyramidal class) Its axial ratio is .4707 : i : 5823 The 
principal forms observed on crystals are P(in), ooP 06(100), 
oo P oo (oio), P 06 (on), oo P2(i2o) and 2P?(i2i) (Fig 99) The crystals 
are often twins (Fig 100), trillings or sixlmgs, with 3? 06 (031) the 
twinning plane, forming pseudohexagonal groupings (Fig 101) Sim- 
ple crystals are usually tabular parallel to oo P So (100), which is striated 
vertically Consequently, in twins this face exhibits stnations arranged 
feather-like. The angle no A iTo=5o 21'. 

The deavage of chrysoberyl is distinct parallel to Poo (on), and 
indistinct parallel to oo P 06 (oio) and oo P 56 (100) Its fracture is 
uneven or conchoidal. Its color is some shade of light green or yellow 
by reflected light. It is transparent or translucent and in some cases is 
distinctly red by transmitted light. It is strongly pleochroic m orange, 



ALUMINATES, FERRITES, ETC 



203 



green and red tints. The mineral is brittle, has a hardness of 8 5 and a 
density of about 3 6 Its refractive indices are a=i 7470, j5=i 7484, 



Four distinct varieties are recognized 

Ordinary, pale green, translucent 

Gem, yellow and transparent 

Alexandrite, emerald-green in color, but red by transmitted light, 
transparent, usually in twins Used as a gem 

Cat's-eye, a greenish variety exhibiting a play of colors (chatoyancy ) 

Before the blowpipe the mineral is infusible It yields the Al reac- 
tion with Co(NOs)2, but otherwise is only slightly affected by the flame 
It is insoluble in acids 

Chrysoberyl is characterized by its crystallization and great hard- 






FIG 99 



FIG ioo 



FIG 101 



FIG 99 Chrysoberyl Crystal with oo P GO 3 100 (a), oo P 55 , oio (b), oo P7, 120 (s), 

2&2 t 121 (), P, in (o) and P oo , on (i). 
FIG 100 Chrysoberjl Thinned about 3? So (031) 
FIG 1 01 Chrysobeiyl Pseudohexagonal Sixlmg Twinned about 3? 5 (031) 

ness It most closely resembles the beryllium silicate, beryt, in appear- 
ance, but is easily distinguished from this by its crystallization. 

Synthesis. Crystals have been made by fusing BeO and AkOs 
with boric acid and then distilling off the boric acid 

Occurrence and Origin Chrysoberyl is found principally in granites 
and crystalline schists and as grains in the sands produced by the erosion 
of these rocks In its original position the mineral is a separation 
from the magma that produced the rocks. 

Localities. Its best known localities are in Minas Geraes, Brazil, 
near Ekaterinburg, Ural; in the Mourne Mts,, Ireland, at Haddam, 
Conn , at Greenfield, N. Y.; at Orange Summit, N. Hamp.; and at 
Norway and Stoneham, Me. The alexandrite comes from Ceylon, where 
it occurs as pebbles, and from the Urals. 



204 



DESCRIPTIVE MINERALOGY 



Braunite (MnMnOs) occurs massive and in crystals. The latter 
are tetragonal (ditetragonal bipyramidal class), 'with a ci 9922, 
They are usually simple bipyramids P(in) Because of the nearly 
equal value of a and c all crystals are isometric in habit The angle 
iiiAii"i 70 7' Twins are common, with POO(IOI) the twinning 
plane Cleavage is perfect parallel to P(III) 

The mineral is brownish black to steel-gray m color and in streak 
Its luster is submetallic Its hardness is 6-6 5 and density 47 It is 
infusible before the blowpipe With fluxes it gives the usual reactions 
for manganese It is soluble in HC1 yielding chlorine 

It occurs in veins with manganese and other ores in Piedmont, Italy, 
and at Pajsberg and various other places m Sweden, where its origin 
is secondary 

Hausmannite (MngMnO^ crystallizes like braumte, but a : <:= 
i : 1 1573 and its crystals are, therefore, distinctly tetragonal m habit 
They are usually simply P(ni) or combinations of P(m) and fP(ii3), 
though much more complicated crystals are known The angle 
niAi7i=6o i' Twins and fourlmgs (Fig 102) are common, with 




FIG 102 Hausmannite. (A) Simple Crystal, P, in (p) and oP, ooi (c) (B) 
Fivelmg Twinned about P oo (101) 



P oo (101) the twinning plane The cleavage is imperfect parallel to 
oP(ooi) The mineral also occurs in granular masses. 

Hausmannite is brownish black Its streak is chestnut brown 
Its hardness is 5-5 5 an d density 4 8. Its reactions are the same as 
those of braumte 

Hausmannite occurs as crystals at Ilmenau, Thurmgia, Ilfdd, 
Harz, and as granular masses in dolomite at Nordmark and several 
other points in Sweden Like braumte it is probably a decomposition 
product of other manganese minerals 



CHAPTER X 

THE NITRATES AND BORATES 
THE OTTBATES 

THE nitrates are salts of nitric acid Only two are of importance 
to us, saltpeter (KNOa) and chile saltpeter (NaNOs) Both are color- 
less, or white, crystalline bodies, both are soluble m water and both pro- 
duce a cooling taste when applied to the tongue The potassium com- 
pound is distinguished from the sodium compound by the flame test 
Both minerals when heated in the closed tube with KHSOi yield red 
vapors of nitrogen peroxide (NCfe) 

Soda Niter (NaNO 3 ) 

Soda niter, or chile saltpeter, is usually m incrustations on mineral 
surfaces or m massi\ e forms It consists of 63 5 per cent N2Os and 
36 5 per cent Na20 

Its crystals are in the ditrigonal scalenohedral class of the hexagonal 
system with an axial ratio of a : c=i : 8297. They are usually rhom- 
bohedrous R(ioTi) m some cases modified by oR(oooi). Apparently 
the mineral is completely isomorphous with calcite (CaCOs) 

Its cleavage is perfect parallel to the rhombohedron. Its hardness 
is under 2, its density about 2.27 and its melting point about 312. 
Its luster is vitreous, color white, or brown, gray or yellow. The min- 
eral is transparent Its refractive indices for yellow light are: w = 1.5854, 

=13369 

Soda niter deflagrates when heated on charcoal and colors the flame 
yellow. When exposed to the air it attracts moisture and finally lique- 
fies. It is completely soluble in three times its own weight of water. 

Occurrence and Localities The principal occurrences of the mineral 
are in the district of Tarapaca, northern Chile, where, mixed 
with the lodate and other salts of sodium and potassium, under the 
name caliche, it comprises beds several feet thick on the surface of rain- 
less pampas, and in Bolivia at Arane under the same conditions. It is 
associated with gypsum, salt and other soluble minerals. Smaller 

205 



206 DESCRIPTIVE MINERALOGY 

deposits are found in Humboldt Co , Nevada, m San Bernardino Co , 
Cal , and in southern New Mexico 

The material is thought to result from the action of microorganisms 
upon organic matter decomposing in the presence of abundant air 

Uses Soda niter is used in the production of nitric acid, and in the 
manufacture of fertilizers and gunpowder About 480,000 tons are 
imported into the United States annually at a cost of $15,430,000 
Most of it comes from Chile 

Since soda niter usually contains sodium lodate as an impurity, the 
mineral is an important source of iodine. 

Niter (KNO 3 ) 

Niter, or saltpeter, resembles soda niter in appearance It gener- 
ally occurs in crusts, in silky tufts and in groups of acicular crystals 
Its crystals are orthorhombic with a b : c= 5910 * i 7011 Their 
habit is hexagonal The principal forms observed on them are oo P(i 10), 
oo P 00(100^, oo P 06(010), oP(ooi), P(in), and a series of brachy- 
domes In many respects the mineral is apparently isomorphous with 
aragonite which is the orthorhombic dimorph of calcite At 126 it 
passes over into an hexagonal (trigonal) form Its cleavage is perfect 
parallel to Poo (on) Its fracture is uneven, its hardness 2 and den- 
sity 2 i Its medium refractive index for yellow light, /3=i 5056 

Niter deflagrates more violently than soda niter and detonates with 
combustible substances It fuses at aboat 335 It colors the blowpipe 
flaine violet It is soluble in water 

Occurrence and Localities The mineral forms abundantly in dry 
soils in Spain, Egypt, Persia, Ceylon and India, where it is produced 
by a ferment, and on the bottoms of caves m the limestones of Madison 
Co , Ky , of Tennessee, of the valley of Virginia and of the Mississippi 
Valley 

Production Most of the niter used in the arts is manufactured, but 
some is obtained from the deposits m Ceylon and m India The 
amount imported in 1912 aggregated 6,976,000 Ib , valued at $226,851 

THE BORAXES 

The borates are salts of bone acid, HsBOs, metaboric acid, HBQz, 
tetrabonc acid, EfeBiOr, hexabonc acid, EUBoOn, and various poly- 
boric acids in which boron is present in still larger proportion The 
metaacid is obtained from the orthoacid by heating at 100, at which 



NITRATES AND BORATES 207 

temperature the former loses one molecule of water, thus. H3BO3 
H2O=HBO2, and the tetraacid by heating the ^ame compound to 160" 
at which temperature 5 molecules of \\ater are lost from 4 molecules ot 
the acid, thus 4H 3 B03-5H 2 O=H 2 B407 Hexabonc acid may be 
regarded as the orthoacid less i| molecules of water, thus. 



Only three of the borates are important enough to be discussed 
here These are borax, a sodium tetraborate (NaoB^Or ioH<zO), cole- 
manite, a hexaborate (CasBoOn slfeO) and boracite, a magnesium 
chloro-polyborate (Mg 5 (MgCl) 2 Bi6Q3o)- Borax and colemamte are 
commercial substances that are produced in large quantities 

All borates and many other compounds containing boron when 
pulverized and moistened with HoSO4 impart an intense yellow-green 
color to the flame If boron compounds are dissolved in hydrochloric 
acid, the solution will turn turmeric paper reddish brown after drying 
at 100 The color changes to black when the stain is treated with 
ammonia. 

Borax (H"a 2 B4O 7 roH 2 O) 

Borax occurs as crystals and as a crystalline cement between sand 
grains around salt lakes, as an incrustation on the surfaces of marshes 
and on the sands in desert regions, and dissolved 
in the water of certain lakes in deserts. It 
occurs also as bedded deposits mterlayered with 
sedimentary rocks 

The composition of borax is 16 2 per cent 
Na 2 0, 36 6 per cent B 2 Qs and 47 2 per cent H^. 

Crystals are monoclmic (prismatic class), with 
a : b : c=i 0995 : J : -5^ 2 9 and 0=73 25' FlG I03 Borax Crystal 
They are prismatic in habit and in general form with P, no (m), 
resemble very closely crystals of pyroxene. P5o,iQo (<*),<?&, 
The principal planes occurring on them are IO _ (6) ' ^ I I ! f) ' 
co P 55 (100), oo P(no), oP(ooi), -P(in) and Jj IZI (a) "* 2p ' 221 
-2P(22i) (Fig. 103). Their cleavage is perfect 
parallel to ooP 60(100), and their fracture concfaoidal. The angle 
noAiTo=93. 

The mineral has a white, grayish or bluish color and a white streak. 
It is brittle, vitreous, resinous or earthy; is translucent or opaque; has 
a hardness of 2-2.5, a density of 1.69-1.72, and a sweetish alkaline taste. 
On exposure to the air the mineral loses water and tends to become white 



208 DESCRIPTIVE MINERALOGY 

and opaque, whatever its color in the fresh condition Its medium 
refractive index for yellow light, 0= i 4686 

Before the blowpipe borax puffs up and fuses to a transparent 
globule Fused with fluonte and potassium bisulphate it colors 
the flame green It is soluble in water, yielding a weakly alkaline 
solution 

Occurrence The principal method of occurrence of the mineral is 
as a deposit from salt lakes in and regions, and as incrustations on the 
surfaces of alkaline marshes overlying buried borax deposits The 
original beds were deposited by the evaporation to dryness of ancient 
salt lakes, and the incrustations were produced by the solution of these 
deposits by ground water, and the nse of the solutions to the surface by 
capillarity. 

Localities. Borax occurs in the water of salt lakes in Tibet, of 
several small lakes in Lake County, and of Borax Lake in San Bernardino 
County in California, and in the mud and marshes around their borders 
It occurs also in the sands of Death Valley in the same State, and in 
various marshes in Esmeralda County, Nevada Other large deposits 
are found in Chile and Peru 

Uses Borax is used as an antiseptic, in medicine, in the arts for 
soldering brass and welding metals, and in the manufacture of cosmetics 
Bone acid obtained from borax and colemamte is employed in the 
manufacture of colored glazes, in making enamels and glass, as an 
antiseptic and a preservative Some of the borates are used as pig- 
ments. 

Production Borax was formerly obtained in the United States, 
especially in California, Oregon and Nevada, by the evaporation of 
the water of borax lakes, by washing the crystals from the mud on their 
bottoms and by the leaching of the mineral from marsh soil At pres- 
ent, however, nearly all the borax of commerce is manufactured from 
colemanite. 

Colemanite (Ca 2 B 6 On sH 2 O) 

Colemamte occurs in crystals and in granular and compact masses 
It is the source of all the borax now manufactured in the United States. 

The formula ascribed to the mineral corresponds to 27 2 per cent 
CaO, 50.9 per cent 6203 and 21 9 per cent H 2 0. As usually found, 
however, it contains a httle MgO and SiCfe. A crystal from Death 
Valley, California, yielded: 

6203=5070; 0*0=27.31, MgO= 10, 



NITRATES AND BORATES 



209 



\1/ 







The mineral crystallizes in the monoclmic system (prismatic class), 
m short, prismatic crystals (Fig 104), with the axial constants a:b:c 
= 7769 . i : 5416 and 0=69 43', The crystals are usualh rich in 
forms Their cleavage is perfect parallel to ocOScloio), and less 
perfect parallel to oP(ooi) Their fracture is uneven The angle 
no A 110=72 4' 

Colemanite is colorless, milky white, yellowish white or gray It 
is transparent or translucent, has a vitreous or adamantine luster, a 
hardness of 4 to 4 5 and a specific 
gravity of 2 4 Its index of refrac- 
tion for yellow light, 18=1.5920 

Before the blowpipe it decrep- 
itates, exfoliates, and partially 
fuses, at the same time coloring 
the flame yellowish green. It is 
soluble in hot HC1, but from the 
solution upon cooling a volumi- 
nous mass of boric acid separates 
as a white gelatinous precipitate 

It is easily distinguished from 
other white translucent minerals, 
except those containing boron, 
by the flame test It is distin- 
guished from borax by its insolu- 
bility in water and from boracite by its inferior hardness and crystal- 
lization 

Syntheses Colemanite has been prepared by treating ulexite 
(NaCaBsOe 8H 2 0) with a saturated solution of NaCl at 70. 

Occurrence and Origin The mineral occurs as indefinite layers 
interstratified with shale and limestones that are associated with basalt 
The rocks contain layers and nodules of colemanite Gypsum is often 
associated with the borate and m some places is in excess. The cole- 
manite is believed to be the result of the action of emanations from 
the basalt upon the limestone. 

Localities Colemanite occurs in Death Valley, California, near 
Daggett, San Bernardino County, and near Lang Station, Los Angeles 
County, and at other points in the same State, and in western Nevada, 
near Death Valley A snow-white, chalky variety (priceite) has been 
found hi Curry County, Oregon, and a compact nodular variety (pander- 
mite) at the Sea of Marmora, and at various points in Asia Minor. 

Preparation Colemanite is at the present time the principal source 



FIG 104 Colemanite Crystals with =cP 
no(m), 3? 5, 301 (v), =*P5c, 100 (a), 
* P , oro (b); oP, ooi fc), -P, in 
(), 2P* 02M), P3b,ouOO, pa, 
210 U), aPoo, 201 (A), 2P, 221 (u) and 
P, In 00 



210 DESCRIPTIVE MINERALOGY 

of borax The crude material as mined contains from 5 per cent to 35 
per cent of anhydrous boric acid (6203) This is crushed and roasted 
The colemamte breaks into a white powder vhich is separated from 
pieces of rock and other impurities by screening, and then is bagged and 
shipped to the refineries where it is manufactured into borax and boracic 
acid 

Production The principal mines producing the mineral in 1912 
were situated in the Death Valley section of Inyo County, near Lang 
Station in Los Angeles County, California, and in Ventura County in 
the same State The total production during the year was 42,315 
tons of crude ore, valued at $1,127,813 The imports of crude ore, 
refined borax and boric acid during the same year were valued at $i 1,200 
The production of the United States m boron acid compounds is 
about half that of the entire world, with Chile producing nearly all 
the rest 

Boracite (Mg 5 (MgCl) 2 Bi 6 O3o) 

Boracite is interesting as a mineral, the form and internal structure 
of which do not correspond, that is, do not possess the same symmetry 
Its crystals have the well marked hextetrahedral symmetry of the iso- 
metric system, but their internal structure, as revealed by their optical 
properties is orthorhombic This is due to the fact that the substance 
is dimorphous Above 265 it is isometric and below that temperature 
orthorhombic Crystals formed at temperatures above 265 assume 
the isometnc shapes. As the temperature falls the substance changes 
to its orthorhombic form, and there results a pseudomorph of ortho- 
rhombic boracite after its isometric dimorph 

It is a salt of the acid which may be regarded as related to boric 
acid as follows. SHsBOs 9H20=H6BsOi5. Ten atoms of hydrogen 
in two molecules of the acid are replaced by Mgs and the other two by 
a(MgCl). The resulting combination is 31 4 per cent MgO, 7 9 per 
cent Cl and 625 per cent BgC^ioi 8(0-Cl=i 9) The mineral 
alters slowly, taking up water, so that some specimens yield water on 
analysis and in the dosed tube (stassfurti e and parasite). 

The forms usually found on the crystals are -(in), ooO(no), 

ooOoo(icx>),--(iIi) (Fig. 105). Usually the positive and negative 

tetrahedrons may be distinguished by their luster, the faces of the posi- 
tive form being brilliant and those of the negative form dull. The 
crystals are isolated, or embedded, and rarely in groups They are 



NITRATES AND BORATES 211 

strongly pyroelectnc with the analogue pole in the negative tetrahedrons. 
The mineral is also found massive 

Boracite is transparent or translucent and is gra\ , yellow, or green 
Its streak is white Its luster is vitreous Its cleavage is indistinct 
parallel to 0(m) and its fracture is conchoidal ^ n ^ 
The mineral is brittle Its hardness is 7 and 
its density 3 Its refractive index , for yellow 
light, = i 667 

Boracite fuses easily before the blowpipe 
with intumescence to a white pearly mass, at 
the same time colonng the flame green With 



copper oxides it colors the flame azure-blue FIG 105 Boracite 
When moistened with Co(NOs)2 it gives the Cr>stal with =cO=c, 
pink reaction for magnesium Some massive /iz;, O, no id), 
forms yield water in the closed tube, in conse- -\ , m (0) and ~ f 
quence of weathering The mineral is soluble _ , , 
inHCl ll 

Boracite is distinguished from other boron salts by its crystallization, 
its lack of cleavage and its much greater hardness The massive vari- 
eties which resemble fine-grained white marble can be distinguished 
from this by the flame coloration, hardness and reaction with HC1 

Syntheses. Crystals have been formed by heating borax, MgCfe 
and a little water at 275, and by fusing borax with a mixture of NaCl 
and MgCk 

Occurrence. Boracite occurs in beds with anhydrite, gypsum and 
saltj and as crystals in metamorphosed limestones 

Localities It is found as crystals in gypsum and anhydrite at 
Luneburg, Hanover, and Segeberg, Holstein, in carnallite at Stassfurt, 
Prussia, and in radiating nodules (stassfurtite) and in massive layers 
associated with salt beds at the last-named locality It is rare in the 
United States 

Uses and Prodwhon Boraute is utilized in Europe as a source of 
boron compounds. Turkey produces annually about 12,000 tons, 



CHAPTER XI 
THE CARBONATES 

THE carbonates constitute an important, though not a very large, 
group of minerals, though one of them, calcite, is among the most com- 
mon of all minerals They are all salts of carbonic acid (EkCOs) Those 
in which all the hydrogen has been replaced by metal are normal salts, 
those in which the replacement has been by a metal and a hydroxyl 
group are basic salts Both groups are represented by common minerals 

The normal salts include both anhydrous salts and salts combined 
with water of crystallization Illustrations of the three classes of car- 
bonates are- CaCOs, calcite, normal salt, Na2COs loEfeO, soda, 
hydrous salt and (Cu OH^COs, malachite, basic salt All carbonates 
effervesce in hot acids The basic salts yield water at a high tempera- 
ture only, the hydrous ones at a low temperature 

The carbonates are all transparent or translucent, and all are poor 
conductors of electricity, Most of them are practically nonconductors 

ANHYDROUS CARBONATES 
NORMAL CARBONATES 

The anhydrous normal carbonates comprise the most important 
carbonates that occur as minerals Most of them are included in a 
single large group whose members are dimorphous, crystallizing in the 
ditrigonal scalenohedral class of the hexagonal system and in the holo- 
hedral division (rhombic bipyramidal class) of the orthorhombic sys- 
tem. The calcium carbonate exists in three forms but only two are 
known to occur as minerals 

CALCITE-ARAGONITE GROUP 

The relation of the dimorphs of this group to one another has been 
subjected to much study, especially with reference to the two forms of 
CaCQs- The orthorhombic form, aragonrie, passes into the hexagonal 
form, calcite, upon heating to about 400. At all temperatures below 
970, calcite is the stable form Moreover, while calcite crystallizes 
from a dilute Solution of.CaCQa in water containing 002 at a low tem- 

212 



CARBONATES 213 

perature, aragomte separates at a temperature approaching that of 
boiling water the more freely, the less C0 2 in the solution Arag- 
omte crystals will also separate from a solution of calcium carbonate, 
if, at the same time, it contains a gram of an orthorhombic carbonate, 
or a small quantity of a soluble sulphate Some of the other carbon- 
ates, for instance, strontiamte (the orthorhombic SrCCfe), pass over 
into an hexagonal form like that of calcite at 700, but again change 
to the orthorhombic form upon cooling For convenience the group 
is divided for discussion into the calcite division and the aragomte 
division 

CALCITE DIVISION 

The calcite division of carbonates includes nine or more distinct 
compounds and a number of well defined \aneties of these Six of the 
compounds are common minerals Afl crystallize in the ditngonal 
scalenohedral class of the hexagonal system and are thus isomorphous 
Their most common crystals have a rhombohedral habit. The names of 
the six common members with their axial ratios are: 

Calcite CaCOs a c=i : 8543 

Magnesite MgCOs =1 : 8095 

Siderite FeCOs =i : 8191 

Khodochrosite MnCOs =i .8259 

Smit\somte ZnCOs =i : 8062 

There is usually also included in the group the mineral dolomite, which 
is a calcium magnesium carbonate in which CaCOs and MgCOs are 
present in the molecular proportions, thus MgCOs CaCOs, or 
MgCa(COs)2 Its crystals are similar to those of calcite and its physical 
properties are intermediate between those of calate and magnesite 
Its symmetry, however, as revealed by etching is tetartohedral (rhom- 
bohedral class). 

The close relationship existing between the members of the group 
(including dolomite) will be appreciated upon comparing the data in 

the following table 

Ref Indices 







H 


SP 


Gr. 


a : c 


loiiAoiu 


tt 


Calcite 


3 




2 


73 


8543 


74 





55' 


I 


6585 


4863 


Dolomite . 


- 3 


5-4 


2 


85 


8322 


73 


o 


45' 


I 


6817 


5026 


Magnesite 


3- 


5-45 


3 


04 


8095 


72 





36' 


I 


717 


515 


Sidente 


3 


5-4 


3 


88 


8191 


73 





o' 


I 


8724 


6338 


Rhodochrosite 


3 


5-45 


3 


55 


8259 


73 





o' 


I 


820 


5973 


Srmthsonite 


5 




4 


45 


8062 


72 





20' 


I 


8i8 


6177 



214 



DESCRIPTIVE MINERALOGY 



Calcite (CaCO 3 ) 

Calcite is one of the most beautifully crystallized minerals known 
Its crystals are very common, and sometimes very large They are 
usually colorless, though sometimes colored, and are nearly always 
transparent Besides occurring in crystals the mineral is often found 
massive, in granular aggregates, in stalactites, in pulverulent masses, 




FIG 106 







FIG 108 




FEG. 107 FIG 109 

FIG. 106. Calcite Crystal with |R, oiTa (e) and s R, joTo (m) Nail-head Spar 

FIG, 107 Calcite Crystal with m and e Prismatic Type 

FIG 108 Calcite Ciystals with m, R, 2131 (p) and R, loli (r) Dog-tooth Spar 
FIG 109 Calcite with r, v, 4R, 4041 (M) and R 8 , 3251 (y) 

in radial groupings, in fibrous masses and in a variety of other forms As 
calate is soluble in water containing COa, it has often been found pseu- 
domorphing other minerals. 

Theoretically, calcite contains 56 per cent CaO and 44 per cent COg, 
but practically the mineral contains also small quantities of Mg, Fe, 
Mn, Zn and Pb, metals whose carbonates are isomorphous with 
CaCO& 

Hie forms that have been observed on calcite crystals are arranged 



CARBONATES 



215 



in such a manner as to produce three distinct types of habit, as fol- 
lows (i) the rhombohedral type, bounded by the flat rhombohedrons, 
R(ioTi), JR(oiT2) and often blunt scale- 
nohedrons, like R 3 (2i3i) and |R 2 (3i45) 
in which the rhombohedrons predominate 
(Fig 106), (2) the pnsmatic type, with 
the pnsm oo P(io7o) predominating, and 
R(oil2) as the principal termination 
(Fig 107), and (3) dog-tooth spar, contain- 
ing the same scalenohedrons as on the first 
type mentioned above with other steeper 
ones and small steep rhombohedral planes 
(Fig 108, 109, no) Nail-head spar con- 
tains the flat rhombohedron |R(oil2) 
with the pnsm oo P(ioTo) (Fig 106). 

Some of the crystals are very compli- 
cated, belonging to no one of the distinct 

types descnbed above, but forming barrel-shaped or almost round 
bodies Over 300 well established forms have been identified on them. 

Twins are common The principal laws are: (i) twinning plane 
oP(oooi), with the vertical axis common to the twinned parts (Fig 
111), (2) twinning plane fR(oiT2), with the two vertical axes inclined 




FIG no Pnsmatic Crystals 
of Calcite Terminated by 
Scalenohedrons and Rhom 
bohedrons from Cumber- 
land, England 





FIG in. 



FIG 112 



FIG in Calate, R* (2131) Twinned about oP (oooi) 
FIG 112 Calcite Twin and Polysynthetic Trilling of R (ion) about R (0112)- 

at an angle of about 52^ (Fig. 112) and (3) twinning plane R(ioTi), 
with the vertical axes inclined 89 14' (Fig. 113), 

Twins of the second dass can easily be produced artificially on cleav- 
age rhombs by pressing a dull knife edge on the obtuse rhombohedral 
edge with sufficient force to move a portion of the mass (Fig. 114). 
The change of position of a portion of the calcite does not destroy its 



216 



DESCRIPTIVE MINERALOGY 



transparency in the least Repeated twinning of this kind is frequently 
seen in marble (Fig 115), ^vhere it gives nse to parallel lamellae 

The cleavage of calcite is so perfect parallel to R that crystals when 





FIG 113 * FIG. 114 

FIG 113 Calcite with m, v and e, Twinned about R (loTi) 
FIG 114 Artificial Twin of Calcite, with JR (oils) the Twinning Plane. 

shattered by a hammer blow usually break into perfect little rhombo- 
hedrons Its hardness is about 3 and its density 2 713 Pure calcite 
is colorless and transparent, but most specimens are white or some pale 

shade of red, green, gray, 
blue, yellow, or even brown 
or black when very impure, 
and are translucent or opaque 
The mineral is very strongly 
doubly refracting, (see p 213) 
It is a very poor conductor of 
electricity. 

The principal vaneties of 
the mineral to which distinct 
names have been given are: 

Iceland spar, the trans- 
parent variety used in the 
manufacture of optical instru- 
ments 

Satin spar, a fine, fibrous 
variety with a satiny luster 
Limestone, granular ag- 
occurnng as rock 




FIG 115 Thin Section of Marble Viewed by 
Polarized Light. The dark bars are poly- 
synthetic twinning lamellae Magnified 5 
diameters. 



masses. 



Marble, a crystalline limestone, showing when broken the cleavage 
faces of the individual crystals. 

Ltike&apkic stone a very fine and even-grained limestone 



CARBOXATES 217 

Stalactites, cylinders or cones of calcite that hang from the roofs of 
caves They are formed by the evaporation of dripping T\ater 

Stalagmites, corresponding cones on the floors of caves beneath the 
stalactites 

Mexican onyx, banded crystalline calcite, often transparent. 
Usually portions of stalactites 

Travertine, a deposit of white or yellow porous calcite produced 
in springs or rivers, often around organic material like the blades 
or roots of grass. 

Chalk, a fine-grained, pulverulent mass of calcite occurring in 
large beds 

In the closed tube calcite often decrepitates Before the blowpipe it 
is infusible It colors the flame reddish yellow and after heating reacts 
alkaline toward moistened litmus paper The mineral dissolves with 
evolution of CO2 in cold hydrochloric acid Its dissociation tempera- 
ture l is 898, though it begins to lose C0> at a much lower temperature 

The reaction with HC1, together \vith the alkalinity of the mineral 
after heating, its softness and its easy cleavage, distinguish calcite from 
all other minerals In massive forms it has been thought that it could 
be distinguished from aragomte by heating its ponder with a httle 
Co(NOs)2 solution Aragomte was thought to become violet-colored 
in a few minutes while calcite remained unchanged, but recent work 
proves that this test cannot be relied upon 

Syntheses Calcite crystals are obtained b\ allowing a solution 
of CaCOs in dilute carbonic acid to evaporate slowly in contact with the 
air at ordinary temperatures If evaporated at from 80 to 100 
ordinary temperatures, or in the presence of a httle sulphate, the ortho- 
rhombic aragonite will form, Calcite is also formed by heating arag- 
onite to 400-470 

Occurrence and Origin. The mineral is widely distributed in beds, 
in veins and as loose deposits on the bottoms of springs, lakes and nvers. 
Its principal methods of origin are precipitation from solutions, the 
weathering of calcareous minerals, and secretion by organisms. 

Calcite is the most important of all pseudomorphmg agencies. It 
forms pseudomorphs after many different minerals and the hard parts 
of animals 

Localities. The most noted localities of .crystallized calcite are: 
Andreasberg in the Harz; Freiberg, Schneeberg and other places in 
Saxony; Kapnik, in Hungary, Traversella, in Piedmont, Alston Moor 

1 The dissociation temperature of a carbonate is that temperature at which the 
pressure of the released CO* equals one atmosphere 



218 DESCRIPTIVE MINERALOGY 

and Egremont, in Cumberland, Matlock, in Derbyshire, and the mines 
of Cornwall, England, Guanajuato, Mexico, Lockport, N Y , Ke- 
weenaw Point, Mich , the zinc regions of Illinois, Wisconsin and 
Missouri, Nova Scotia, etc 

Iceland spar is obtained in the Eskefjord and the Breitifjord in 
Iceland Travertine is deposited from the waters of the Mammoth 
Hot Springs, Yellowstone National Park It occurs also along the 
River Arno, near Tivoli, Rome 

Uses. Calcite has many important uses In the form of Iceland 
spar, on account of its strong double refraction, it is employed in optical 
instruments for the production of polarized light Calcite rocks are 
used as building and ornamental stones They are employed also as 
fluxes in smelting operations, as one of the ingredients in glass-making 
and in the manufacture of lime, cement, whiting, and in certain printing 
operations. Limestone is also used as a fertilizer 

Production The calcite rock marketed in the United States during 
1912 was valued at about $44,500,000 It was used as follows In 
concrete, $5,634,000, in road and railroad making, $12,000,000, as a 
flux, $10,000,000, as building and monumental stone, $12,800000, 
in sugar factories, $335,000, as riprap, $1,183,000, for paving, $279,000, 
and for other uses, $2,400,000 Moreover, the value of the Portland 
cement manufactured during the year amounted to $67,017,000, the 
quantity of lime made to $13,970,000, the value of the hydrated 
lime to $1,830,000, and of sand-lime brick to $1,170,884 The quantity 
of limestone required for these manufactures is not known, but it was 
very great. 

Magnesite (MgCO 3 ) 

Magnesite usually occurs in fine-grained white masses Crystals 
are rare Pure magnesite consists of 52 4 per cent CCb and 47 6 per 
cent MgO. It usually, however, contains some iron carbonate 

Magnesite is completely isomorphous with calcite Its cleavage is 

perfect parallel to R(ioTi). Its hardness is about 4 and the density 3 i. 

The mineral is transparent or opaque. It varies in color from white 

to brown, but always has a white streak Its dissociation temperature 

o 

is 445 - 

Magnesite behaves like calcite before the blowpipe It effervesces 
in hot hydrochloric acid and readily yields the reaction for magnesia 
with Co(NQs)2 It is most easily distinguished from the latter mineral 
by its density, by the fact that it does not color the blowpipe flame with 
the yellowish red tint of calcium and does not effervesce in cold HCL 



CARBONATES 210 

Synthesis Magnesite crystals may be obtained by heating MgSO 
in a solution of XajCOa at 160 in a closed tube 

Occurrence and Origin Magnesite usualh occurs in \ ems and masses 
associated with serpentine and other magnesium rocks irom which it 
has been formed by decomposition It is often accompanied by brucite 
talc, dolomite and other magnesium compounds It has recently been 
described as occurring also in a distinct bed near Mohave, CaL, inter- 
stratified with cla> s and shales It is thought that in this case it ma} 
have been precipitated fron* solutions of magnesium salts by Xa^COs 

Localities The mineral is found abundantly m many foreign local- 
ities and at Bolton, Mass , Bare Hills, near Baltimore, Md , and in 
Tulare Co., Cal , and near Texas, Penn The largest deposits are in 
Greece and Hungary 

Uses. Magnesite is employed very largely in the manufacture of 
magnesite bricks used for lining converters in steel works, in the lining 
of kilns, etc , m the manufacture of paper from wood pulp, and in mak- 
ing artificial marble, tile, etc From it are also manufactured epsom 
salts, magnesia (the medicinal preparation) and other magnesium com- 
pounds, and the carbon dioxide used in making soda water 

Production All of the magnesite mined in the United States comes 
from California, where the yield was 10,512 tons in 1912, valued at 
$105,120. Most of the magnesite used in the United States is imported 
from Hungary and Greece In 1912, 14,707 tons of crude material 
entered the country and 125,000 tons of the calcined product, the total 
value of which ^as $1,370,000 

Siderite (FeCO 3 ) 

Siderite is an important iron ore, though not as much used as formerly 
It is found crystallized and massive, in botryoidal and globular forms 
and m earthy masses 

In composition the mineral is FeCOa, which is equivalent to 62 i 
per cent FeO (48 2 per cent Fe) and 37 9 per cent COj- Manganese, 
calcite and magnesium are also often present in it. 

Crystals are more common than those of magnesite. They fre- 
quently contain the basal plane and the steep rhombohedrons 8R(o8Si) 
and sRfesi). R(ioli) and |R(oiT2) are common The faces 
of the rhombohedron are frequently curved. Compare (Fig 125.) 

The cleavage of Siderite is like that of the other minerals of this 
group. Its hardness is 3 5-4 and density 3 85. In color the mineral 
is sometimes white, but more frequently it is some shade of yellow or 
brown Its streak is white Most specimens are translucent. 



220 DESCRIPTIVE MINERALOGY 

In the closed tube siderite decrepitates, blackens and becomes mag- 
netic It is only slcroly affected by cold acids but it effervesces briskly 
in hot ones 

Siderite is distinguished from the other carbonates by its reaction 
for iron 

The mineral changes on exposure into limonite and sometimes into 
hematite or even into magnetite 

Synthesis Crystals of sidente may be obtained by heating a solu- 
tion of FeSCU with an excess of CaCOs at 200 

Occurrence and Origin The mineral is often found accompanying 
metallic ores in veins It occurs also as nodules in certain clays and in 
the coal measures. In some cases it appears to be a direct deposit from 
solutions In others it is a result of metasomatism and m others is an 
ordinary weathering product 

Localities The crystallized variety is found at Freiberg, in Saxony, 
at Harzgerode, in the Harz, at Alston Moor, and in Cornwall, Eng- 
land, and along the Alps, in Styna and Cannthia Cleavage masses 
are present in the cryolite from Greenland 

Workable beds of the ore are present m Columbia Co , and at Rossie, 
in St. Lawrence Co , N Y , in the coal regions of Pennsylvania and 
Ohio, and in clay beds along the Patapsco River, in Maryland The 
massive or nodular ore from clay banks is known as ironsto? e The 
impure bedded sidente interstratified with the coal shales is known 
as black-band ore 

Production. Only 10,346 tons of sidente were produced in the United 
States during 1912, all of it coming from the bedded deposits in Ohio 
This was valued at $20,000 

Rhodochrosite (MnCO 3 ) 

This mineral sometimes occurs in distinct crystals of a rose-red 
color, but it is usually found in cleavable masses, in a compact form, 
or as a granular aggregate Sometimes it is m incrustations It is 
not of commercial importance in North America 

Pure manganese carbonate containing 61 7 per cent MnO and 38 3 
per cent CQs is rare The mineral is usually impure through the addi- 
tion of the carbonates of iron, calcium, magnesium or zinc 

The most prominent forms on crystals of rhodochrosite are R(ioYi), 
|R(oil2), ooP2(ii2o), oR(oooi) and various scalenohedrons 

Its cleavage is perfect parallel to R The mineral is brittle Its 
hardness is about 4 and its density about 3.55 Its luster is vitreous, 
and its color red, brown, or yellowish gray. Its streak is white When 



CARBONATES 221 

heated it begins to lose CCb at about 320": but its dissociation temper- 
ature is 632 

The mineral is infusible, but T\hen heated before the blowpipe it 
decrepitates and changes color When treated in the borax bead it 
gives the violet color of manganese, and \\hen fused with soda on char- 
coal it yields a bluish green manganate It dissoh es in hot hydro- 
chloric acid 

There are but fe\v minerals resembling pure rhodochrosite m appear- 
ance From all of these, except the silicate, rhodonite ip 3801, it is 
distinguished by its reaction for manganese It is distinguished from 
rhodonite by its hardness, its cleavage and its effervescence with acids 
The impure varieties are very like some forms of siderite, from which, 
of course, the manganese test will distinguish it. 

Synthesis Small rhombohedrons of rhodochrosite have been pro- 
duced by heating a solution of MnSQ* with an excess of CaCCfe at 200 
in a closed tube 

Occurrence and Origin Rhodochrosite occurs in veins associated 
with ores of silver, lead, copper and other manganese ores and in bedded 
deposits It is the result of hydrothermal or contact metamorphism, 
and of weathering of other manganese-bearing minerals 

Localities. The mineral is found at Schemmtz, in Hungary, at 
Nagyag, in Transylvania, at Glendree, County Clare, Ireland, where it 
forms a bed beneath a bog, at Washington, Conn , in a pulverulent 
form, at Franklin, N J , at the John Reed Mine, Ahconte, Lake Co , 
and at Rico, Colo , at Butte City, Mont , at Austin, Xev., and on 
Placentia Bay, Newfoundland The Colorado and Montana specimens 
are well crystallized 

Uses The mineral is mined with other ores of manganese. Occa- 
sionally it is employed as a gem stone. 

Smithsonite fZnCO 3 ) 

Smithsomte, or "dry-bone ore," is rarely well crystallized. It 
appears as druses, botryoidal and stalactitic masses, as granular aggre- 
gates and as a fnable earth. 

In ZnCOs there are 64 8 per cent ZnO and 35 2 per cent CCte Smith- 
somte usually contains iron and manganese carbonates, often small 
quantities of calcium and magnesium carbonates and sometimes traces 
of cadmium A specimen from Marion, Arkansas, gave: 

ZnO CdO FeO CaO CuO CCfe CdS Sift> Total 

64 12 .63 .14 .38 tr. 34-68 25 06 100 26 



222 DESCRIPTIVE MINERALOGY 

The mineral is closely isomorphous with calcite, R(ioTi), iR(oiT2), 
4R(404i), ooR2(ii2o), oR(oooi) and R 3 (2i3i) being present on many 
crystals The R faces are rough or curved 

Its cleavage is parallel to R(ioli). Its hardness is 5 and its density 
about 4 4. The luster of the mineral is vitreous, its streak is white and 
its color white, gray, green or brown It is usually translucent, occa- 
sionally transparent When heated to 300 for one hour it loses all of 
its C0 2 

When heated in the closed tube CC>2 is driven off, leaving ZnO as a 
yellow residue while hot, changing to white on cooling The mineral 
is infusible before the blowpipe If a small fragment be moistened with 
cobalt nitrate solution and heated in the oxidizing flame it becomes 
green on cooling When heated on charcoal a dense white vapor is 
produced. This forms a yellow coating on the coal, which, when it 
cools, turns white If this be moistened with cobalt nitrate and reheated 
in the oxidizing flame it is colored green. 

The above reactions for zinc, together with the effervescence of the 
mineral in hot hydrochloric acid distinguish smithsomte from all other 
compounds. 

Smithsomte forms pseudomorphs after sphalerite and calcite and is 
pseudomorphed by quartz, hmomte, calamine and goethite 

Synthesis Microscopic crystals of smithsomte may be produced by 
precipitating a zinc sulphate solution with potassium bicarbonate and 
allowing the mixture to stand for some time. 

Occurrence. Smithsomte occurs in beds and veins in limestones, 
where it is associated with galena and sphalente and usually with cala- 
mine (p 396) It is especially common in the upper, oxidized zone of 
veins of zinc ores and as a residual deposit covering the surface of weath- 
ered limestone containing zinc minerals 

Localities The mineral is found at Nerchinsk, Siberia, Bleiberg, 
in Cannthia; Altenberg, Aachen, Province of Santander, Spain, at 
Alston Moor and other places in England, at Donegal, in Ireland, at 
Lancaster, Penn , at Dubuque, Iowa, in Lawrence and Marion Coun- 
ties, Arkansas; and in the lead districts of Wisconsin and Missouri (see 
galena and sphalerite). 

The Wisconsin and Missouri localities are the most important ones 
in North America. Here the ore occurs in botryoidal, in stalactitic 
and in earthy, compact, cavernous masses of a dull yellow color incrusted 
with druses of smithsonite crystals, of calamine and of other minerals, 
principally of lead This is the variety known as " dry bone " 

Uses The mineral was formerly an important ore of zinc, being 



CARBONATES 223 

mined alone for smelting It is no\v mined only in connection with 
calamine and other zinc ores, and all are worked up together. A trans- 
lucent green or greenish blue variety occurring at Laurium, Greece, 
and at Kelly, New Mexico, is sometimes employed for ornamental pur- 
poses. About $650 worth of the material from New Mexico was utilized 
as gem material in 1912 

ARACOX1TE DIVISION 

This division of the carbonates includes the orthorhombic (rhombic 
bipyramidal) dimorphs of the members of the calcite group which, 
together, form a well characterized isodimorphous group. The carbon- 
ate of calcium is found well crystallized in both dmsions, but the other 
carbonates are common to one only They actually occur in both divi- 
sions, but they are found as .common members of one and only as 
isomorphous mixtures with other more common forms in the other 
Thus, barium carbonate is a common orthorhombic mineral under the 
name of uithente It occurs also with CaCOs in mixed crystals under 
the name bancalcite, or neotype, \*hich is hexagonal. (See also p. 212 
and p 213 ) 

The common members of the aragonite division are: 

Aragomte CaCOs Sp Gr. = 2 936 a : b : c= 6228 : i 

Stronfaamte SrCOs =3 706 == 6090 : i 

Witkente BaCOa =4 325 = 5949 : i 

Cerussite PbCOs ac 6 574 = 6102 : i 7232 

Aragonite (CaCOs) 

Aragomte occurs m a great variety of forms. Sometimes it is in 
distinct crystals, but more frequently it is in oolitic globular and reni- 
form masses, in divergent bundles of fibers or of needle-like forms, in 
stalactites and in crusts. 

In composition aragonite is like calcite. It often contains small 
quantities of the carbonates of strontium, lead or zinc. 

Crystals*are often acicular with steep domes predominating. Some 
of the simplest crystals consist of oop(uo), ooP 00(010), fP 00(032), 
Poo (on), 4?(44i), 9P(9Qi) and ooP2(i2o) (Fig. 116). Twinning is 
common. The twinning plane is often ooP(iio). By repetition this 
gives nse to pseudohexagonal forms, resembling an hexagonal prism and 
the basal plane (see Figs 117 and 118), The angle no A i "10=63 48'. 

The cleavage of aragonite is distinct parallel to oo p 06 (oio) and 
indistinct parallel to oo P(no). Its hardness is 3.5-4 and density about 
2 93 Its luster is vitreous and its color white, often tiiigcd with gray, 



7204 
7266 



224 



DESCRIPTIVE MINERALOGY 



green or some other light shade Its streak is white and the mineral is 
transparent or translucent Its indices of refraction for yellow light are 
a=SI j^oo, 7=1 6857 At 400 it passes over into calcite 

Before the blowpipe aragomte whitens and falls to pieces Other- 
wise its reactions are like those of caktte, from which it can be distin- 





\ 



'" ui 



FIG 116 



FIG 117 

FIG 116 Aragomte Crystal with o P, no (m), oo P So , oio (6) and P So , on 
FIG 117 Aragomtc Twin and Trilling Twinned about co P (no) 





A 

FIG 1 18 Trilling of Aragomte Twinned about <*>P (no) (A) Cross-section 
(B) Resulting pseudohexagonal group, resembling an hexagonal prism and 
basal plane 

guished by its crystallization, its lack of rhombohedral cleavage and its 
density 

Synthesis Solutions of CaCOs in dilute HaCOs form crystals of 
aragomte when evaporated at a temperature of about 90 In general, 
hot solutions of the carbonate deposit aragomte, while cold solutions 
deposit calcite If the solution contains some sulphate or traces of 
strontium or lead carbonates, mixed crystals consisting principally of 
the aragomte molecule are formed at ordinary temperature, 

Occurrence and Origin Aragomte occurs in beds, usually with 
gypsurn. It is also deposited from hot waters and from coid waters 



CARBONATES 225 

containing a sulphate (as from sea water) The pearly layer of oyster 
shells and the body of the shells of some other mollusca are composed 
of calcium carbonate crystallizing like aragomte Aragomte is often 
changed by paramorphism into calcite, pseudomorphs of which after 
the former mineral are quite common 

Localities The mineral is found at Aragon, Spain, at Bilm, in 
Bohemia, in Sicily, at Alston Moor, England, and at a number of 
other places in Europe It occurs in groupings of interlacing slender 
columns (fios /em), m the iron mines of Styria Stalactites are abundant 
at Leadhills, Lanarkshire, Scotland, and a silky fibrous variety known as 
satmspar, at Dayton, England 

In the United States crystallized aragomte occurs at Mine-la-Motte, 
Mo , and in the lands of the Creek Nation, Oklahoma Flos fern has 
been reported from the Organ Mts , New Mexico, and fibrous masses 
from Hoboken, N J , Lockport, Edenville and other towns in New York 
and from Warsaw, 111 

Strontianite (SrCO 3 ) 

In general appearance and in its manner of occurrence strontianite 
resembles aragomte Its crystals are often acicular in habit though 
repeated twins are common The angle no A iTo=62 41' 

The composition of pure strontianite is SrO=7o i, C02=2g 9, but 
the mineral usually contains an admixture of the barium and calcium 
carbonates 

Strontianite is brittle, its hardness is 3 5-4 and its density 3 7 

Before the blowpipe strontianite swells and colors the flame with a 
crimson tinge It dissolves in hydrochloric acid The solution im- 
parts a crimson color to the blowpipe flame When treated with sul- 
phuric acid it yields a precipitate of SrSO* Its refractive indices for 
yellow light are a= i 5199, 7=1 668 Its dissociation temperature is 

"SS 

Aragomte, witherite (BaCOs) and strontianite are so similar in ap- 
pearance and in general properties that they can be distinguished from 
one another best by their chemical characteristics They are all sol- 
uble in hydrochloric acid and these solutions impart distinctive colors 
to the blowpipe flame (see p 477) 

Syntheses Crystals of strontianite are obtained by precipitating 
a hot solution of a strontium salt by ammonium carbonate, and by cool- 
ing a solution of SrCOs in a molten mixture of NaCl and KC1 

Occurrence, Strontianite occurs in veins in limestone and as an 



226 DESCRIPTIVE MINERALOGY 

alteration product of the sulphate (celestite) where this is exposed to the 
weather It is probably in all cases a deposit from water 

Localities Strontiamte is the most common of all strontian com- 
pounds It frequently occurs as the filling of metallic veins It forms 
finely developed crystals at the Wilhelmme Mine near Munstei, West- 
phalia At Schohane, N Y , it occurs as crystals and as gianular masses 
in nests in limestone It is found also at other places in New York, in 
Mifflm Co , Penn , and on Mt Bannell near Austin, Texas. 

Uses Strontium compounds are little used m the arts The 
hydroxide is employed to some extent m refining beet sugar and the 
nitrate m the manufacture of " red fire " Othei compounds aie used 
m medicine All the strontium salts used in the United States arc 
imported 

Witherite (BaC0 3 ) 

Withente differs very little in appearance or in manner of occurrence 
from aragomte Its crystals are nearly always m repeated twins that 

have the habit of hexagonal pyramids (Fig. 
119) The angle noAiTo62 46', 

When pure the mineral contains 77 7 pei 
cent BaO and 22 3 per cent C02 

It is much heavier than the calcium car- 
bonate, its density being 43 Its hardness 
FIG 119 wuhcriic Twinned is 3 to 4 Its refractive mdc\ foi yellow 
about COP (no), thus Im.- llght / s ==I740 i ls (hbboaation tenii mu- 
tating Hexagonal Combina- ture Jg 

It dissolves readily in dilute hydrochloric 

acid with effervescence, and from thib solution, even when dilute, sul- 
phuric acid precipitates a heavy white precipitate of BaSO-t, winch, 
when heated m the blowpipe flame, imparts to it a yellowish green 
color 

Witherite is distinguished from the other carbonates by its crys- 
tallization, and the color it imparts to the blowpipe flame. 

Syntheses Crystals are produced by precipitating a hot solution of 
a barium salt with ammonium carbonate, and by cooling a molten 
xnagma composed of NaCl and BaCO? 

Locahfoes Witherite is not a very common mineral in the United 
States, but it occurs in large quantity associated with lead minerals in 
veins at Alston Moor, in Cumberland and near Hexham, in Northum- 
berland, England Some of the crystals found in these places measure 
as much as six inches in length 





CARBONATES 



227 



Its best known locality in the United States is Lexington, Kentucky, 
where the mineral is associated with the sulphate, bante 

Uses It is used to some extent as a source of banum compounds 
The importations of the mineral during 1912 aggregate $25,715 

Cerussite (PbC0 3 ) 

Cerussite generally occurs in crystals and in granular, earthy and 
fibrous masses of a white coloi 

The pure lead carbonate contains C02=i6 5 and PbO=835j but 
the mineral usually contains in addition some ZnCOa 







FIG 1 20 



FIG 121 



FIG 122 



FIG 120 Cerussite Crystal with cop no (w), ooPoo , 100 (0), ooPoo, oio (6), 
P, in (p), oo P^, 130 ( r ), 2 Poo, 021 (i), Pw,on (fc), JPoo, 012 (x) and 
oP, ooi (c) 

FIG 121 Cerussite Tnlhng Twinned about *> P(no) 

FIG 122 Cerussite Tnllmg Twinned about o 



Its simple crystals are tabular combinations of oo P(i 10) , oo P 08 (oio) 
oo Poo (100) and various brachydomes (Fig 120), and these are often 
twinned in such a way as to produce six rayed stars (Fig 121), or other 
symmetrical forms (Fig 122) Groups of interpenetrating crystals 
are also common The angle iioAiio=62 46'. 

The color of the mineral is usually white, but its surface is frequently 
discolored by dark decomposition products Its luster is adamantine 
or vitreous and its hardness is 3-3 5 Its density =6.5 Its refractive 
indices for yellow light are a = i 8037, = 2 0763, 7=2 0780 

The mineral is dissolved by nitric acid with effervescence and by 
potassium hydroxide Before the blowpipe it decrepitates, turns yellow 
and changes to lead oxide On charcoal it is reduced to a metallic 
globule, and yields a white and yellow coating 



228 DESCRIPTIVE MINERALOGY 

Cerussite is not easily confused with other minerals It is well char- 
acterized by its high specific gravity, its reaction for lead, and is dis- 
tinguished from the sulphate (anglesite) by effervescence with hot acids 

Syntheses Crystals have been obtained by heating lead formate with 
water in a closed tube, and by treatment of a lead salt by a solution of 
ammonium carbonate at a temperature of iso-i8o 

Occurrence and Origin The mineral occurs at all localities at which 
other lead compounds are found, since it is often produced from thes* 




FIG 123 Radiate Groups of Cerussite on Galena from Park City Distrid, Utah. 
(After J M BoHlwell) 

latter by the action of the atmosphere and atmospheric water It is, 
therefore, usually found m the upper portions of veins 

Locates Cerussite crystals of great beauty are found m many of 
the lead-producing districts of Europe and also at Phoemxville, Penn ; 
near Union Bridge, m Maryland, at Austin's Mines, Wythe Co., Vir- 
ginia, and occasionally in the lead mines of Wisconsin and Missouri, 
In the West it occurs at Leadville, Colo , at the Flagstaff and other 
mines m Utah (Fig 123), and at several different mines in Arizona. 

Uses, It is mined with other lead compounds as an ore of the metal 



CARBONATES 229 

Dolomite (MgCa(CO 3 ) 2 ) 

Dolomite is apparently isomorphous with calcite but the etch 
figures on rhombohedral -faces prove it to belong m the trigonal 
rhombohedral class It occurs as crystals and in all the forms charac- 
teristic of calcite except the fibrous 

Nearly all calcite contains more or less magnesium carbonate, but 
most of the mixtures are isomorphous with calcite and magnesite 
When the ratio between the two carbonates reaches 5435 per cent 
CaCOs 45 65 per cent MgCOs, which is equal to the ratio between 
the molecular weights of the two substances, or in other words when the 
two carbonates are present in the compound in the ratio of one molecule 
to one molecule, the mineral is called dolomite The calculated com- 
position of dolomite (MgCa(COs)2) is 30 4 per cent CaO, 217 per cent 
MgO and 47 8 per cent CCte 

The crystals of dolomite are usually rhombohedral combinations of 
the rhombohedron R(ioli) with the scalenohedron 
R 3 (2i3i) (Fig 124), and its tetartohedral forms, 
and often the prism oop2(ii2o) and the basal 
plane Its axial ratio is a:c**i m 8322 Twins 
are not rare, with oR(oooi) and R(ioTi) the 
twinning planes The R planes are often curved, 
frequently with concave surfaces (Fig 125) The 

angle loli A7ioi = 73 . ^ , 

rro. i i j i -j. - i. ni FIG 124 Dolomite 

The cleavage of dolomite is perfect parallel crystal with 4R 

to R The mineral is brittle Its hardness is 40 ^ T y^ an d O p' 
3 5-4 and density 2 915 Its luster is vitreous or oooi (c) 
pearly and its color white, red, green, gray or 
brown Its streak is always white and the mineral is translucent or 
transparent Its refractive indices for yellow light are w= 16817, 
= i 5026 The important varieties recognized are 
Pearlspar, with curved faces having a pearly luster 
Granular or saccharoidd, including many marbles and magne'San 
limestones 

Dolomifoc limestone, including much hydraulic limestone 
Many dolomites are intermixed with the carbonates of iron, manga- 
nese, cobalt or zinc and these are known as ferriferous dolomite, etc 

Dolomite behaves like calcite before the blowpipe and in the closed 
tube It, however, dissolves only slowly, if at all, m cold hydrochloric 
acid, except when very finely powdered, though dissolving readily with 
effervescence in hot acid 




230 DESCRIPTIVE MINERALOGY 

The reaction toward cold acid and its greater hardness easily dis- 
tinguish dolomite from calcite It is distinguished from magnetite by 
the flame reaction 

Occurrence and Origin Dolomite, like the calcium carbonate, occurs 
crystallized m veins, and as granular masses forming gicat beds of rock 
It is a precipitate from solutions and a metasomatic alteration product 
of calcite 

Localities Its crystals are present at many places, among them 
Bex, in Switzerland, Traversella, in Piedmont, Guanajuato, in Mexico, 
Roxbury, in Vermont, Hoboken, N J., Niagara Palls, the Quarantine 




FIG 125. Group of Dolomite Crystals from Jophn, Mo Flat Rhombohedrons with 

Curved Faces 

Station, and Putnam, N. Y , Joplin, Mo , and Stony Pouil, N C. It 
is also very widely spread as beds of dolomitic limestone 

Uses Dolomite is used for many of the purposes served by calcite, 
indeed, much of the material used as marble, limestone, etc , contains a 
large percentage of magnesium carbonate It is not, however, used as a 
flux or m the manufacture of Portland cement, nor as a source of lime 

Ankerite (Ca(Mg Fe) (003)2) is a ferruginous dolomite. It is an 
isomorphous mixture of the carbonates of calcium, magnesium and iron, 
in which the FeCOa replaces a part of the MgCOs in dolomite It is 
usually in rhombohedral crystals, with the angle xoTi A 1101-73 48' 
Its color is white, gray or red and its streak is white Its hardness 
=3 5-4, and its density = 2 98 It also occurs m coarse and fine-grained 
granular masses, Ankente is infusible before the blowpipe. In the 



CARBONATES 231 

closed tube it darkens and when heated on charcoal it becomes mag- 
netic It occurs in veins, especially those containing iron minerals 
It has been found at Antwerp and other places m northern New York. 

CALCIUM-BARIUM CARBONATES 

Carbonates of the general composition CaBa(COs)2 occur (i) as a 
series of mixed crystals isomorphous with caicite under the name hart- 
calctte, (2) as a series of mixed crystals isomorphous with aragomte 
known as alstomte or bromhte, and (3) a typical double salt, barytocalctte, 
which is monoclmic Both alstomte and barytocaicite occur in veins 
of lead ores and of bante 



Barytocaicite, CaBa(COs)2 is monoclmic (prismatic class), with 
a : b . c~ 7717 i 6255 and =73 52' It forms crystals bounded 
by oo P 66 (100), ccP(no), oP(ooi), and a series of clmopyramids, of 
which 2P2 (12!) and sP$ (i 5!) are common It also occurs massive Its 
perfect cleavage is parallel to ooP(no) The mineral is white, gray, 
greenish or yellowish Its streak is white, hardness =4 and sp gr = 
3 665 It is transparent or translucent Before the blowpipe frag- 
ments fuse on thin edges, and assume a pale green color, due to the 
presence of a little manganese The mineral is soluble in HC1 Its 
principal occurrence is Alston Moor, Cumberland, England. 

BASIC CARBONATES 

The basic carbonates are salts in which all or a portion of the hydro- 
gen of carbonic acid is replaced by the hydroxides of metals There 
are only three minerals belonging to the group that need be referred to 
here Two are copper compounds One is the bright green malachite 
and the other the blue azunte The composition of the former may be 

CuOHv 

represented by the formula ;>C03, and that of the latter by 

CuOH/ 

CuOHv 

Cu==(COs)2. Both are used to some extent as ores of the metal, 
CuOH/ 

though their value for this purpose is not great at the present time 
They may easily be distinguished from all other minerals by their 
distinctive colors, by the fact that they yield water in the closed tube 
and by their effervescence with acids The third mineral (hydrozincite) 
is a white substance that occurs as earthy or fibrous incrustations on other 
zinc compounds. Its composition corresponds to 2ZnCOs sZn(OH)2 




232 DESCRIPTIVE MINERALOGY 

Its hardness = 2-2 5 and its specific gravity is about 3 7 Only the two 
copper compounds are described m detail 

Malachite ((CuOH) 2 CO 3 ) 

Malachite usually occurs in fibrous, radiate, stalactitic, granular 
or earthy, green masses, or as small drusy crystals covering other copper 
compounds The mineral contains, when pure, 19 9 per cent CO2, 
71 9 per cent CuO and 8 2 per cent KbO 

Well defined crystals are usually very small monoclmic prisms (mon- 
oclmic prismatic class), with an a\ial ratio 8809 i 
4012 and #=6i 50' Their predominant forms 
are ooPoo(ioo), ooPo>(oio), ooP(no), and 
oP(ooi) Contact twins arc common, with 
oo P 60(100) the twinning plane (Fig 126) The 
angle no A iTo= 75 40' 

The puie mineral is bright green in color and has 
a light green stieak It possesses a vitieous luster, 
FIG 126 -Malachite but this becomes silky m fibrous marc* and dull 
Crystal with ?, m massive specimens Crystals are translucent 
no (w), ooPw, and massive pieces aic opaque. Translucent 
ioo (a), and oP, pieces are pleochroic in yellowish green and dark 
cot (c) Twinned green tmts Thc clcavage 1S perfcct paid ud to 

oP(ooi) Thc haidness of malachite is 3 5-4, and 
its density about 3 9 Its refractive index, /3, for yellow light ==i 88 

Malachite turns black and fuses befoic the blowpipe and tinges the 
flame green With NaaCOs on charcoal it yields a copper globule. It is 
difficultly soluble m pure water, but is easily dissolved m water con- 
taining C02 It is soluble with effervescence in HCl and its solution 
becomes deep blue on the addition of an excess of ammonia. When 
heated in a closed glass tube, it gives an abundance of water. Boiled 
with water it turns black and loses its COa 

Malachite, on account of its characteristic color, may be easily dis- 
tinguished from all other minerals but some varieties of turquoise and 
a few copper compounds, such as atacamite (p 144) It may be dis- 
tinguished from all of these by its effervescence with acids 

Synthesis. Malachite crystals have been obtained with the form of 
natural crystals by heating a solution of copper carbonate m ammonium 
carbonate 

Occurrence and Origin Malachite is a frequent decomposition 
product of other copper minerals, being formed rapidly in moist places. 



CARBONATES 233 

It occurs abundantly in the upper oxidized portions of veins of copper 
ore, where it is associated with azurite, cuprite, copper, kmomte and the 
sulphides of iron and copper, often pseudomorphmg the copper minerals 
The green stain noticed on exposed copper trimmings of buildings is 
composed in part of this substance 

Localities The mineral occurs in all copper mines At Chessy, 
France, it forms handsome pseudomorphs after cuprite In the United 
States it has been found in good specimens at Cornwall, Lebanon Co , 
Penn , at Mineral Point, Wisconsin, at the Copper Queen Mine, Bisbee, 
and at the Humming Bird Mine, Morenci, Arizona, and in the Tintic 
district, Utah. 

Uses In addition to its use as an ore of copper the radial and mass- 
ive forms of malachite are employed as ornamental stones for inside 
decoration The massive forms are also sawn into slabs and polished 
for use as table tops and are turned into vases, etc 

Production As malachite is mined with other copper compounds, 
the quantity utilized as an ore of the metal is not known The amount 
produced in the United States during 1912 for ornamental purposes was 
valued at $1,085 This, however, included also a mixture of malachite 
and azurite. 

Azurite (Cu(CuOH)2(CO 3 ) 3 ) 

Azurite is more often found in crystals" than is malachite. It occurs 
also as veins and incrustations and in massive, radiated, and earthy 





FIG 127 Azurite Crystals with oP, oot (c), -Pco, 101 (<r), ooPoo, 100 (a), 
P, YII (*), oo P, no (), -2P, 221 (A), jPa, 243 (d) and P & , on (/) 

forms associated with malachite and other copper compounds. Its 
most frequent associate is malachite, into which it readily alters 

In composition azurite is 25 6 per cent CCh, 69 2 per cent CuO, and 
5 2 per cent EfeO It changes rapidly to malachite, and sometimes is 
reduced to copper 

The crystals are tabular, prismatic, or wedge-shaped monochmc 
forms (monochmc prismatic dass), with an axial ratio a . b : c= 8501 : 
i : r 7611, and P~Bj 36', They are usually highly modified, 58 or 



234 DESCRIPTIVE MINERALOGY 

more different planes having been identified on them The predominant 
ones are oP(ooi), POO(IOI), ooP(no), -2P(22i) and oopoo(ioo). 
(Fig 127 ) The angle no A 1*0=80 40' 

The mineral is dark blue, vitreous, and translucent or transparent, 
and is pleochroic in shades of blue It is brittle Its streak is light 
blue, its hardness 3 5-4 and density 3 8 Its cleavage is distinct parallel 
to Poo (on) 

The blowpipe and chemical reactions for azunte are the same as 
those for malachite By them the mineral is easily distinguished from 
the few other blue minerals known 

Synthesis Crystals have been formed on calcile by allowing frag- 
ments of this mineral to lie in a solution of CuNOj for a year or more 

Occurrence The mineral occurs in the oxidized zone of copper veins. 
It is an intermediate product m the change of other coppei compounds 
to malachite 

Localities Azunte occurs m beautiful crystals at Cressy, France, 
near Redruth, in Cornwall, at Phoenix ville, Pcnn , at Mineral Point, 
Wis , at the Copper Queen Mine, Bisbce, Aiu , at the Mammoth 
Mine, Tintic district, Utah, at Hughes's Mine, California, and at many 
other copper mines in this country and abroad 

From Morenci, Ariz , Mr Kunz describes specimens consisting of 
spherical masses composed of alternating layers of malachite and 
azunte, which, when cut across, yield surfaces banded by alternations of 
bright and dark blue colors 

Uses Azurite is mined with other copper minerals as an ore of cop- 
per It is also used to a slight extent as an ornamental stone (see mal- 
achite). 

HYDROUS CARBONATES 

The hydrous carbonates are salts containing water of crystalliza- 
tion They are carbonates of sodium or of this metal with calcium or 
magnesium Some of them occur in abundance in the waters of salt or 
bitter lakes, but very few are known to occur m any large quantity in 
solid form Among the commonest are: 

Soda or natron Na2COa xoBfeO monochmc 

Trona HNas (C0s)2 - aEfeO monoclmic 

Gayliissite NagCa(C03)2 sEfeO monoclimc 

Hydromagnestie Mg^OH^COaVsBfeO orthorhombic 



These minerals occur either m the muds of lakes or as crusts upon the 
mud or upon other minerals, 



CARBONATES 235 

Natron occurs only in solution and in the dry mud on the borders 
of lakes 

Trona, or urao, (HNa 3 (C0 3 )2 2H 2 0) is found as crystals in the 
mud of Borax Lake, California, as a massive bed in Churchill Co., 
Nevada, and as thin coatings on rocks in other 
places. Its crystallization is monochnic (pns- ^ c 
matic class), with the axial ratio, 2 8426 : i . V 7 

29494 and 18=76 31' Its crystals are usually \ * -> 

bounded by oP(ooi), ooP 66(100), -P(m) and FIG 128 Trona Ciys- 
+P(Tn) (Fig 128) Fibrous and massive forms tal with oP, ooi (c), 
are common The mineral has a perfect cleavage p * > I0 (fl ) and 
paraUel to oo P 60 (100) It is gray or yellowish +P ' m (o) 
and has a colorless streak It has a vitreous luster, a hardness of 
2 5-3, and a density of 2 14 It is soluble in water and has an alkaline 
taste It exhibits the usual reactions for Na and for carbonates 

Gaylussite (Na2Ca(COs)2 5H 2 0) also occurs as crystals in the 
muds of certain lakes, especially Soda Lake, near Ragtown, Nevada, 
and Menda Lake, Venezuela, and in clays under swamps in Railroad 
Valley, in Nevada Its crystals are monochnic 
(prismatic class) with a : b : c=i 4897 : i : 1 4442 
and 0=78 27' They are usually bounded by 
oo P(no), P oo (on), and ^P(Ti2) (Fig 129), or by 
these planes and oP(ooi) and oo P 66 (100). They 
are either prismatic because of the predominance 
of Pob(oii) and oP(ooi), or are octahedral m 
habit because of the nearly equal development of 
P ob (on) and oo P(iio). Their cleavage is perfect 
FIG 1 29 -Gaylussite para ]i e l to ooP(no) 

Crystal with oop, ^ ^^ . g ^^ ^ Uowish and trans ^ 

no (m), Poo ,011 J 

(e)and JP,Ti2 (r). l ucent I ts hardness is 2-3 and density 199 

It is very brittle When heated m the closed 

tube it decrepitates and becomes opaque It loses its water at 100 

In the flame it melts easily to a white enamel and colors the flame yellow 

It is partially soluble in water, leaving a white powdery residue of CaCOs 

and is entirely soluble in acids with effervescence The mineral occurs 

in such large quantity in the clays underlying swamps in Railroad Valley, 

Nevada, that its use has been suggested as a source of NagCOs- 




CHAPTER XII 
THE SULPHATES 

THE sulphates are salts of sulphuric acid A large number are 
known to occur in nature but many of them are dissolved in the waters 
of salt lakes Of the remaining ones only a few are very common 
These may be divided into an anhydrous normal group, a basic group and 
a hydrated group In addition, there are several minerals that are 
sulphates mixed with chlorides or carbonates 

All the sulphates that are soluble in water give the test for sulphuric 
acid When heated with soda on charcoal they are reduced to sulphides 
The mass when placed on a silver com and moistened with a drop of 
water or of hydrochloric acid partly dissolves and stains the silver dark 
brown or black 

The sulphates when pure are all white and transparent, and are all 
nonconductors of electricity 

ANHYDROUS SULPHATES 
NORMAL SULPHATES 

The anhydrous normal sulphates ha\c the general formula R/2S04 
or R"S04 The most common ones are sulphates of the alkaline earths 
and lead They belong in a single group which is orthorhombic The 
few less common ones are sulphates of the alkalies or of the alkalies 
and alkaline earths Only two of the latter are described* 

Glauberite (Na 2 Ca(SO 4 )2) 

Glaubente may be regarded as a double salt of the composition 
NaaS04 CaSO/t, which requires 511 per cent Na2S04 and 48.9 per cent 
CaS04 The mineral contains 22 3 per cent Na20, 20 i per cent CaO 
and 57 6 per cent SOs 

It nearly always occurs in monochmc crystals (prismatic class), 
with an axial ratio i 2209 . i i 0270 and #=67 49'. The most fre- 
quent combination is oP(ooi), P(ni), ooP(no), ooP 06(100), 
3P3(3iT) and +P(u7), with oP(ooi) prominent (Fig 130) The 
cleavage is perfect parallel to oP(ooi) The angle noAiTo s =96 58'. 

236 



SULPHATES 



237 




Glaubente is yellow, gray or brick-red m color, is transparent or 
translucent and has a white streak, a vitreous luster and a conchoidal 
fracture Its hardness is 2 5-3 and its specific 
gravity about 28 It is brittle It is partly 
soluble m water, imparting to the solution a 
slight saltiness The red color of many speci- 
mens is due to the presence of inclusions 

Before the blowpipe the mineral decrepi- 
tates, whitens and fuses easily to a white 
enamel, at the same time coloring the flame FIG 130 Glaubente Crys- 
yellow It is soluble m HC1 and in a large talwithoP.ooi (), <*p, 
quantity of water In a small quantity of 
water it is partially dissolved with loss of 
transparency and the production of a deposit of 

It sometimes alters to calcite 

Occurrence Glaubente is associated with rock salt and other de- 
posits from bodies of salt water It is found 
at Villa Rubia, m Spam, and elsewhere 
in Europe, and m the Rio Verde Valley, 
Arizona and at Borax Lake, California 



no (m), oo P oo , 100 (a) 
and P, in (s) 




FIG 131 Thenarditc Crystal 
with oo P, no (w), P, nT 
(o), IPS, 106 (0 and oP, 
ooi (c) 



Thenardite (Na2S04) occurs as ortho- 
rhombic crystals in the vicinity of salt 
lakes, and m beds associated with other 
lake deposits Its crystals ha\e an axial ratio 5976: i i 2524 
They are commonly prismatic but those 
from California are tabular and are bounded 
by ooP(uo), oP(ooi), P(iiT), P 60(106), 
and ooPw(ioo) (Fig 131) Twins are 
common (Fig 132) 

The mineral is colorless, white or reddish 
and has a salty taste Its hardness is 2-3 
and Its specific gravity 2 68 Its inter- 
mediate refractive index is i 470 It is 
readily soluble in water. It occurs in exten- 
sive deposits in the Rio Verde Valley, Ari- 
zona, and as crystals at Borax Lake, Cali- 
fornia and on the shores of salt lakes in 
Central Asia and South America. 




FIG 132 Thenardite 
Twinned about P 06 (on) 
Forms same as m Fig. 131 
and oo P oo , 100 (a) 



238 DESCRIPTIVE MINERALOGY 



BARITE GROUP 

The bante group includes the sulphates of the alkaline earths and 
lead They are all light colored minerals with a nonmetallic luster 
They all crystallize in the orthorhombic system (bipyramidal class), 
and all have a hardness of about 4 The minerals comprising this group, 
with their axial ratios, are 

Anhydnte CaSO* a b : c= 8932 ' i i 0008 
Bante BaS04 =8152 i 1 3136 

Celestite SrS(>4 = 7790 i . i 2800 

Angleute PbSQi = 7852 : i . i 2894 

Anhydrite (CaSO 4 ) 

Calcium sulphate is dimorphous The natural compound, anhy- 
drite, is orthorhombic bipyramidal In addition to this, there is another 
which passes over into anhydrite when shaken for a long time with boiling 
water It is produced by dehydrating gypsum at about 100 When 
moistened it combines with water and passes back to gypsum It is 
probably tnclmic It is unstable under the conditions prevailing at 
the earth's suiface and is, therefore, not found as a mineral 

Anhydrite occurs usually m fibrous, granular or massive forms, not 
often in crystals When crystals occur they are commonly prismatic or 
tabular m habit 

In composition the mineral is 58 8 per cent SOa and 41 2 per cent 
CaO 

Its crystals are usually bounded by the three pinacoids oP(ooi), 
oo P 60(100), oo p 06(010) and P(ni), 2P2(i2i), 3P3(i3i), POO(IOI) 
and Poo (on) The prismatic types are usually elongated parallel to 
the macroaxis The angle noAiTo=83 41' 

Anhydrite fuses quite easily before the blowpipe and colors the flame 
reddish yellow It is very slightly soluble in water but is completely 
dissolved in strong sulphuric acid It cleaves parallel to the three pm- 
acoids yielding rectangular fragments. Its hardness is 3-3 5 and den- 
sity about 2 93 Its luster is vitreous m massive pieces and its color 
white, often with a distinct tinge of blue, gray or red. In small frag- 
ments it is translucent, but in large masses it is opaque Its refractive 
indices for yellow light are = i 5693, 7=1 6130 

It is distinguished from the other sulphates by its specific gravity 
and the color it imparts to the blowpipe flame 



SULPHATES 239 

Synthesis Its crystals have been produced by slowly evaporating a 
solution of gypsum in HfoSCX 

Occurrence Anhydrite occurs as crystals implanted on the minerals 
of ore veins, cis beds of granular masses associated with gypsum, and as 
crystalline masses in layers associated with rock salt the two having 
been deposited by the evaporation of salt waters 

Localities The mineral is found at the salt mines of Stassfurt, in 
Germany, Hail, in Tyrol, Bex, in Switzerland, in the ore veins of 
Andreasberg, m Harz, Bleiberg, m Carmthia, and at many other places 
m Europe At Lockport, N Y , and at Nashville, Tenn , it occurs as 
crystals lining geodes m limestone, and at the mouths of the Avon and 
St Croix Rivers m Nova Scotia it forms large beds associated with 
gypsum 

Uses Finely granular forms of the mineral are used for ornamental 
purposes, and as a medium for the use of sculptors The massive variety 
is occasionally employed as a land plaster to enrich cultivated soils 

Barite (BaSO 4 ) 

Bante, or heavy spar, usually occurs crystallized, though it is also 
often found massive and in granular, fibrous and lamellar forms It is 
a common mineral associated with sulphide ores as a gangue 

The mineral is sometimes pure but it is usually intermixed with the 
isomorphous calcium and strontium sulphates The pure mineral con- 
tains 34 3 pei cent SOs and 65 7 per cent BaO As usually mined it 
contains SiOa, CaO, MgO, AlgOa, FegOa and in some instances PbS2 
(galena) 

The simple crystals are usually tabular or prismatic in habit. The 
tabular forms are commonly bounded by oP(ooi), ooP(no) and the 
domes, P 66 (101), |P ob (102), 2P 06 (021), and P 06 (on), and sometimes 
P(ni) and oo Poo (100) (Fig. 133), The prismatic forms are usually 
elongated m the direction of 
the a axis, and are bounded 
by the same planes as the 
tabular crystals (Fig 134) FlG I33 Bante Crystals with oop, J10 (m), 
Complex crystals are also iPoo, 102 (d), PoS,oii (0) and oP, ooi (c) 
abundant They are often 

beautifully supplied with planes, the total number known on the 
species being about 100 The angle noAiio^T 80 22?' 

The cleavage of bante is perfect parallel to oP(ooi) and oo P(no) 
It is brittle Its hardness is about 3 and its density about 4 5 The 




240 DESCRIPTIVE MINERALOGY 

mineral is white, often with a tinge of yellow, biown, blue, 01 red 
It is transparent or opaque and its streak is white Its refi active 
indices for yellow light die a= i 6369, 7= i 6491 

Before the blowpipe bante decrepitates and fuses, at the same time 

coloring the flame yel- 
lowish green The fused 
mass reacts alkaline to 

lltmus paper Jt 1S m " 





The mineral barite is 
FIG 134 -Bante Crystals with m, d, o and c as m distinguished from the 
Fig 133 Also coPoo, zoo (a), P, m 60 and ^ 

P2, 122 (y) l / 

high specihc gravity and 

the color it imparts to the blowpipe flame 

Syntheses Crystals have been made by heating precipitated barium 
sulphate with dilute HC1 in a closed tube at 150, and by cooling a fusion 
of the sulphate in the chlorides of the alkalies or alkaline earths 

Occurrence and Origin Bante is a common vein-stone It con- 
stitutes the gangue of many ore veins, particularly those of copper, 
lead and silver. It is found also as a replacement of limestone, which, 
when it weathers, leaves the barite in the form of fragments and noduleb 
in a residual clay, and as a deposit in hot spnngs. In all cases it is 
believed to be a deposit from solutions 

Localities Barite occurs abundantly in England, Scotland, and on 
the continent of Europe Crystals are found at Cheshire, Conn ; at 
DeKalb, St Lawrence Co , N Y , at the Phoenix Mine in Cxbarrus 
Co,, N C , and near Fort Wallace, New Mexico Massive barite m 
pieces large enough to warrant polishing is found on the bank of 
Lake Ontario, at Sacketts Harbor, N Y It constitutes the filling of 
veins at many different places, more particularly in the southern Appa- 
lachians and m the Lake Superior region, 

Preparation Much of the mineral that enters the trade in the 
United States is obtained from the deposits in residual clay The rough 
material is washed, hand picked, crushed, ground and treated with 
sulphuric acid. The acid dissolves most of the impurities and leaves 
the powdered mineral white 

Uses The white varieties of the mineral are ground and the powder 
is used in making paints The mineral is also employed in the manu- 
facture of paper, oilcloth, enameled ware, and m the manufacture of 
barium salts, the most important of which is the hydroxide, which is 
employed m refining sugar. 



SULPHATES 241 

The colored massive varieties, more especially stalactitic and fibrous 
forms, are sawn into slabs, polished and used as ornamental stones 

Production The quantity of bante mined in the United States 
during 1912 was over 37,000 tons, valued at $153,000 The principal 
producing states are Missouri, Tennessee and Virginia. The imports 
in the same year were about 26,000 tons of crude material, valued at 
$52,467 and 3,679 tons of manufactured material, valued at $26,848 
Besides, there were imported $70,300 worth of artificial barium sul- 
phate and about $280,000 worth of other barium salts, exclusive of 
witherite. 

Celestite (SrSO*) 

Celestite occurs in tabular prismatic crystals, in fibrous and some- 
times in globular masses Though usually white, it often possesses a 
bluish tinge, to which it owes its name 

The theoretical composition of the mineral is 43 6 per cent 80s 
and 56 4 per cent SrO, but it often contains small quantities of the 
isomorphous Ca and Ba compounds 

Many celestite crystals are very similar in habit to those of bante. 





FIG. 135 Celestite Crystals with oo p, no (w), iPoo, 102 (<Q, J Poo, 104 (r), 
oo P oo , oio (&), P oo , on (0) and oP, ooi (c) 

Tabular forms are perhaps more common (Figs. 135), Occasionally, 
pyramidal crystals are bounded by PiJ(i44), oP^(ioo), Poo (on) 
and oP(ooi) These often have rounded edges and curved faces and 
thus come to have a lenticular shape. The angle no A iTo= 75 50' 

The cleavage of the mineral is perfect parallel to oP(ooi) and almost 
perfect parallel to oo P(IIO) Its hardness is about 3 and its specific 
gravity 3 95. Its luster and streak are like those of barite. Its color 
is often pale blue and sometimes light red, but pure specimens are 
white or colorless. Its refractive indices for yellow light are: = i 6220, 
7=1 6237 

Before the blowpipe celestite reacts like barite except that it tinges 
the flame crimson This crimson color may be obtained more dis- 
tinctly by fusing a little powder of the mineral on charcoal in the reduc- 



242 DESCRIPTIVE MINERALOGY 

mg flame and dissolving the resulting mass in a small quantity of hydro- 
chloric acid, then adding some alcohol and igniting the mixture 

Syntheses Crystals of celestite are produced in ways analogous 
to those in which bante crystals are formed 

Occurrence and Ongin Celestite occurs in beds with rock salt and 
gypsum, as at Bex, Switzerland, associated with sulphur, as at Gir- 
genti, Italy, and in crystals and grams scattered through limestone, 
as at Strontian Island, Lake Erie, and in Mineral Co , W Va , or 
as crystals lining geodes in the same rock It is also sometimes found 
as a gangue in mineral veins In some instances it was deposited by 
hot waters, in others by cold waters, and in others it was concentrated 
by the leaching of strontium-bearing limestones by atmospheric water 

Production and Uses Although the mineral occurs in large quan- 
tity at a number of places in the United States and Canada it is not 
mined A small quantity of the strontium oxide is annually imported 
Strontium salts, prepared from celestite in part, aie used in the manu- 
facture of fireworks and medicines and m refining sugar. 

Anglesite (PbSOt) 

Anglesite occurs principally as crystals associated with galena and 
other ores of lead, but is found also massne, and in granular, stalactitic 
and nodular forms 

The theoietical composition of the mineral demands 73 6 per cent 
PbO and 26 4 S0 3 

Its orthorhombic crystals are usually prismatic or isomctnc in habit 
Tabular habits are less common than in bante and celestite The 
principal forms occurring are ooPcfc (100), <*>P(iio), iPoo (102), and 
other macrodomes, P oo (on) and various small pyramids, with oP(ooi), 
m addition, on the tabular crystals (Figs ij6, 137, 138), The angle 
no A iTo=76 i6J' 

The cleavage of anglesite is distinct parallel to oP(ooi) and oo P(i 10) 
Its fracture is conchoidal The mineral is white, gray or colorless and 
transparent, and is often tarnished with a gray coating. It has an 
adamantine or residuous luster, is bnttle and has a colorless streak 
Its hardness is 2 5-3 and sp gr 6 3-6 4. Impure varieties may be 
tinged with yellow, green or blue shades and m some cases may be 
opaque Its refractive indices for yellow light are = i 8771, 7 i 8937. 

Before the blowpipe anglesite decrepitates It fuses m the flame of 
a candle On charcoal it effervesces when heated with the reducing 
flame and yields a button of metallic lead In the oxidizing flame it 



SULPHATES 



243 



gives the lead sublimate The mineral dissolves m HN0 3 with dif- 
ficulty 

The mineral is characterized by its high specific gravity and the 




FIG 136 FIG 137 

FIG 136 Ynglesilc Crystal with w P, no (m), ooPw, 100 (a), oP, ooi (c), 

JP, 112 (/) and Pi, 122 (y) 

FIG 137 \nglcsitc Crystal with /;/, a and y as in Fig 136 Also oopoo, 
cio (bj, P oo , on (o), P, in (s) and JP oo , 102 (d) 

reaction for lead. It is distinguished from (.erussrte by the reaction for 
sulphur and the lack of effervescence with HC1 

Syntheses Crystals of anglesite have been made by methods anal- 
ogous to those used in the preparation of bante crystals 

Occurrence The mineral occurs as an alteration product of galena, 

mainly in the upper portions of veins of 

lead ores Under the influence of solu- 
tions of carbonates it changes to cerus- 
site 

Localities It is found in Derby- 
shire and Cumberland, in England, 
near Siegen, in Prussia, m Australia and 
in the Sierra Mojada, m Mexico In the 
United States crystals occur at Phoenix- 

ville, Penn , in the lead districts of the Mississippi Valley, and at 
various points in the Rocky Mountains 

Use*. It is mined with other lead compounds as an ore of this metal 

BASIC SULPHATES 

Although several basic sulphates are known as minerals, only two 
are of importance One, brochantite, is a copper compound found, with 
other copper minerals, in the oxidized portions of ore veins, and the 
other, alumte, is a double salt of aluminium and potassium. This min- 




FIG 138 Anglesite Crystal with 
m, y, c and d as in Figs 136 and 
137 Also iP 63 , 104 (Q and P?, 
144 (x) 



244 DESCRIPTIVE MINERALOGY 

eral is one of a series of compounds forming an isomorphous group, with 
the general formula (R'"(OH) 2 ) 6 R'2(S0 4 )4 or (R'''(OH) 2 )oR''(SOi)i, 
in which R'"=A1 or Fe, R' 2 =K 2 , Na 2 or H 2 and R"=Pb 

Alumte ((A1(OH) 2 ) 6 K 2 (S0 4 )4) 

Alunite, or aiumstone, is a comparatively rare mineral, but, because 
of its possible utilization as a source of potash, it is of considerable in- 
terest It has long been used abroad as a source of potash alum 

The mineral, when pure, contains 38 6 per cent 863, 37 o per cent 
Al 2 0s, ii 4 per cent K 2 and 13 o per cent EkO, which corresponds to 
the formula given above, or if written in the form of a double salt 
3(A1(OH) 2 ) 2 S04 K 2 S04 The chemical composition of a crystalline 
specimen from Marysville, Utah, is as follows 



S0 3 Al 2 0j Fe 2 3 P20f, K 2 Na 2 H 2 0+ H 2 0- Si0 2 Total 
38 34 37 18 tr 58 xo 46 33 12 90 09 22 too 10 

Alunite occurs in hexagonal crystals (ditrigonal scalenohedral class), 
with an axial ratio of i i 252 The natural crystals are nearly always 
simple rhombohedrons, R(ioTi), or R modified by other rhombohedrons 
and the basal plane Because the angle between the rhombohcdral 
faces is about 90 (90 50') , the habit of the crystals is cubical The 
mineral also occurs massive, with fibrous, granular or porcelain-like 
structure 

Alunite is white, pink, gray or red, and has a white streak It is 
transparent or translucent and has a vitreous or nearly pearly luster. 
Its cleavage is distinct parallel to oP(oooi), and it has an uneven, con- 
choidal or earthy fracture Its hardness ib 3 5-4 and its density = 
26-275. Its indices of refraction for yellow light are: sas iS92, 
<o=i 572 

Before the blowpipe the mineral decrepitates, but is infusible In 
the closed tube it yields water and at a high temperature sulphurous and 
sulphuric oxides Heated on charcoal with Co(NOs) 2 it gives the blue 
color characteristic of Al 2 0a It also gives the sulphur reaction It is 
insoluble in water but is soluble in H 2 S04 When ignited it gives off 
all its water and three-quarters of its S04, the other quarter remaining 
in &2S04 When the igmted residue is treated with water, the potas- 
sium sulphate dissolves and insoluble Al 2 0s is left. It is upon this 
latter reaction that the economic utilization of the mineral depends, 

The mineral is characterized by its color and hardness together 
with the reactions for AljHgO and sulphuric acid 



SULPHATES 245 

Synthesis Crystals have been made by heating an excess of alu- 
minium sulphate with alum and water at 230 

Occurrence anl Ongm The mineral occurs m seams or veins in 
acid lavas It is thought to have been formed in some instances by 
the action of sulphurous vapors upon the rock forming the vein walls, 
in other instances by direct precipitation from ascending magmatic 
waters, and in others by the action of descending BfeSC^ 

Localities The principal known occurrences of alumte are at 
Tolfa, Italy, at Bulla Delah, New South Wales, on Milo, Grecian 
Archipelago, and at Mt Dore, France 

In the United States it is found with quartz and kaolin in the 
Rosita Hills, and the Rico Mts,, Colo , in the ore veins at Silverton 
and Cripple Creek, Colo , as a soft white kaolin-like material in the 
ore veins at Goldfield, Nev , as a crystalline constituent in the rocks 
at Goldfield, Nev , and Tres Cerntos, Cal , and in the form of a great 
vein of comparatively pure material at Marysville, Utah 

Uses In Australia alumte is calcined and then heated with dilute 
sulphuric acid. The mixture is then allowed to settle and the clear 
solution is drawn off and cooled Alum crystallizes The mother liquor 
which contains aluminium sulphate, after further treatment with the 
calcined mineral, is evaporated and the aluminium salt separated by 
crystallization In the United States it is now (1916) being utilized 
as a source of potash and aluminium 

Brochantite ((CuOH)2S04 2Cu(OH)2) occurs in groups of small 
prismatic crystals, in fibrous masses and in drusy crusts Its crystal- 
lization is orthorhombic with a b -.7739 i ; 4871 and the angle 
1 10 A no =75 28' Cleavage is perfect parallel to oopas (oio). The 
mineral is emerald-green to blackish green and its streak is light 
green. It is transparent or translucent, and its luster is vitreous, 
except on cleavage planes where it is slightly pearly Its hardness is 
3 5-4 and density 3 85 In the closed tube it decomposes, yielding 
water and, at a high temperature, sulphuric acid. It gives the usual 
reactions for copper and sulphuric acid Brochantite occurs in the 
upper portions of copper veins at many places, in some of which it was 
formed by the interaction between silicates and solutions of copper 
salts. In the United States it has been foi}nd at the Monarch Mine, 
Chaffee Co , Colorado, at the Mammoth Mine, Tmtic District, Utah, 
and in the Clifton-Morenci Mines, Arizona, 



246 DESCRIPTIVE MINERALOGY 

HYDROUS SULPHATES 

The hydrous sulphates comprise a numbei of sulphates combined 
with water Among them are the normal salts miralnhte or glauber 
salt (Na2S04 loEfeO), gypsum (CaSQi 2H/)), the epwmilc and inclan- 
tertte groups (R // S0 4 7H 2 0), chakanttnte (CuS04 sEbO), md the 
alum group (R'A1(S0 4 )2 i2H 2 0), kiesente (MgSOi H 2 O), polyhalite 
(K2MgCa2(S(X)4 H20), and a number of basic compounds Several 
of them are of considerable economic importance, They are separated 
into a normal group and a basic group, 

HYDRATED NORMAL SULPHATES 

The hydrated normal sulphates occur in crystals, and most of them 
are found also in beds mterstratified with other compounds that arc 
known to have been precipitated by the evaporation of sea water or the 
water of salt and bitter lakes All are soluble in water 

Mirabdite, or glauber salt, (Na2SOt loHaO) is a white, trans- 
parent to opaque substance occurring m monoclmic crystals or as 
efflorescent crusts Its hardness is i 5-2 and specific gravity i 48 It 
is soluble in water and has a cooling taste When exposed to the air it 
loses water and crumbles to a powder Mirabihte occurs at the hot 
springs at Karlsbad, Bohemia and is obtained from the water of many 
of the bitter lakes m California and Nevada Its crystals are deposited 
from a pure solution of Na2S04 If the solution contains NaCl, how- 
ever, thenardite (Na2S04) deposits 

Kieserite (MgS(>4 H20) occurs commonly m granular to compact, 
massive beds mterstratified with halite and other soluble salts at Stass- 
furt, Germany, and at other places where ocean water has been evap- 
orated. It is believed to have resulted from the partial desiccation of 
epsomite (MgS04 ?H20), though it may be deposited from a solution 
of MgSO* m the presence of MgCfe. Kiesente is white, gray, or yellow- 
ish, and is transparent or translucent It forms sharp bipyraimdal 
monoclmic crystals Its hardness is 3 and its density 2 57* In the 
presence of water it passes over into epsomite and dissolves, yielding a 
solution with a bitter taste. Large quantities are utilized in the fer- 
tilizer industry 

When exposed to the air it becomes covered with aa opaque crust* 



SULPHATES 



247 



Gypsum (CaSO 4 2H 2 0) 

Gypsum is the most important of all the hydrous sulphates It 
occurs in massive beds a'vociated with limestone, m crystals, in finely 
granular aggregates and in fibrous masses, under a great variety of 
conditions 

Theoretically, it consists of 46 6 per cent 80s, 32 5 per cent CaO and 
20 9 per cent EfeO, but usually it contains also notable quantities of other 
components, especially Fe203, AbOa and 8162 Clay is a common im- 
purity in the massive varieties 

The analyses of two commercial gypsums follow 

CaSCXt H 2 Si0 2 A1 2 3 CaC0 3 MgC0 3 Total 
78 40 19 96 35 12 56 57 99 96 
78 51 20 96 05 08 ii 99 71 



Dillon, Kans 
Alabaster, Mich 



The crystals are monoclmic (prismatic class), with a : b ^=.6895 : 
i 4132 and j8=8i 02' They are usually developed with a tabular 
habit due to the predominance of oo P OD (oio) The prism oo P(iio), 






FIG 139 FIG 140 

FIG 139 Gypsum Crystals with wP, no (), ooPoo, oio (ft), P, in (/) and 



FIG 140 Gypsum Twinned about oo P 55 (100) Swallow-tail Twin Form m t 

I and b as in Fig 139 

and pyramid +P(ixI) are also nearly always present (Fig 139). Often 
the +P faces are curved, producing a lens-shaped body Twinning is 
very common, giving rise to two types of twinned crystals In the most 
common of these oo P 56 (100) is the twinning plane and the resulting 
twin has the form of Fig 140 In the second type -P 66 (101) is the 
twinning plane (Fig. 141) Forms of this type are frequently bounded 
by +P(iiT), -P(iii), |P oo (103), and OP65 (100) When the side 



248 



DESCRIPTIVE MINERALOGY 





faces are curved the well known arrowhead twins result (Fig 141) 

The angle noAiTo=68 30' 

The mineral possesses a good cleavage parallel to oo P $> (oio) 

yielding thin inelastic fohae, another parallel to +P(Tn) and a less 

perfect one parallel to oo P 66 (100) 
It is white, colorless and transpar- 
ent when pure, gray, icd, yellow, 
blue or black when impure Its 
hardness is i 5-2 and sp. gr =2 32 
The luster of crystals is pearly on 
oo P ob (oio) and on other surfaces 
vitreous Massive varieties are often 
dull The refractive indices for yel- 
low light are, a= 1.5205, 0= 1.5226, 

FIG 141 Gypsum Twinned about ^*~J S 2 9 

-P5(ioi) Forms <*>POO, 100 In the closed tube the mineral 
(a), -P, in (/), P, nl () and gives off watei and falls into a white 
J P 55 , Io 3 (e) Arrow head Twm powder (see p 238) It colors the 

flame yellowish red and yields the sul- 
phur test on a silver coin. It is soluble m about 450 pts of water and 
is readily soluble in HC1 When heated to between 222 F and 400 F 
it loses water and disintegrates into powder, which, when ground, 
becomes " plaster of Pans " This, when moistened with water, again 
combines with it and forms gypsum The crystallization of the mass 
into an aggregate of interlocking crystals constitutes the " set." 

Gypsum is distinguished from other easily cleavable, colorless min- 
erals by its softness and the reactions for S and EfeO. 

The varieties of gypsum generally recognued are. 

Syenite, the transparent crystallized variety, 

Safanspar, a finely fibrous variety, 

Alabaster, a fine-grained granular variety, and 

Rock-gypsum, a massive, structureless, often impure and colored 
variety. 

Gypsiie is gypsum mixed with earth 

Syntheses Crystals of gypsum separate from aqueous solutions of 
CaSO* at ordinary temperatures, and also from solutions saturated 
with Nad and MgCk Some of these are twinned. 

Occurrence and Origin Gypsum forms immense beds interstrati- 
fied with limestone, clay and salt deposits where it has been precipitated 
by the evaporation of salt lakes Its crystals occur around volcanic 
vents, where they are produced by the action of sulphuric acid on cal- 



SULPHATES 249 

careous rocks. They are also found isolated in clay and sand, and in 
limestone, wherever this rock has been acted upon by the sulphuric acid 
resulting from the weathering of pynte Gypsum also occurs in veins 
and is found in New Mexico in the form of hills of wind-blown sand 

Localities Crystals are found m the salt beds at Bex, Switzerland, 
in the sulphur mines at Girgenti, Sicily, and at Montmar-tre, France 
In the United States they occur at Lockport, N Y , in Trumbull Co , 
Ohio, and in Wayne Co , Utah, in limestone, and on the St Mary's 
River, Maryland, in clay 

Extensive beds occur in Iowa, Michigan, New York, Virginia, Ten- 
nessee, Oklahoma and smaller deposits in many other states, and wind- 
blown sands in Otero Co , New Mexico 

Uses Crude gypsum is used in the manufacture of plaster, as a 
retarder in Portland cement, and as a fertilizer under the name of land 
plaster The calcined mineral is used as plaster of Pans and in the 
manufacture of various wall finishing plasters, and certain kinds of 
cements Small quantities are used in glass factories, and as a white- 
wash, a deodorizer, to weight phosphatic fertilizer, as an adulterant in 
candy and other foods, and as a medium for sculpture 

Production The quantity of gypsum mined in the United States 
during 1912 aggregated 2,500,757 tons, valued at $6,563,908 in the form 
in which it was sold Of this amount, 441,600 tons of crude material, 
valued at $623,500 were sold ground, and 1,731,674 tons, valued at $5,- 
940,409, were calcined The output of New York was valued at $1,241,- 
500, that of Iowa at $845,600 and of Ohio at $812,400 

After the United States the next largest producer is France with a 
product in 1910 of 1,760,900 tons, valued at $2,942,600 and Canada with 
525,246 tons, valued at $934,446 

EPSOMITE AND VITRIOL GROUPS 

These groups comprise minerals with the general formula RSO-i 7HkO, 
in which R=Mg, Zn, Fe, Ni, Co, Mn and Cu Isomorphous mix- 
tures indicate that the compounds are diomorphous, and that the 
group is, therefore, an isodimorphous group. The group is separable 
into two divisions, of which one, the epsomite group, crystallizes in the 
bisphenoidal class of the orthorhombic system with axial ratios approx- 
imating i : i ' ,565 The other division, the vUriol 9 or mdanterite, 
group crystallizes in the prismatic class of the monochmc system with 
axial ratios approximating 1 18 ' i ' i 53 and ft approximating 75 
Only the magnesium compound among the pure salts is known to crys- 
tallize in both systems. Crystals separated from a saturated solution 




250 DESCRIPTIVE MINERALOGY 

are orthorhombic, while those separated from a supersaturated solution 
are monoclimc Other salts occur in isomorphous mixtures in both 
systems All members of the group are soluble in water and all occur as 
secondary products formed by decomposition of other minerals. 

Epsomite (MgSO 4 7H 2 0) 

Epsomite, or Epsom salt, usually occurs in botryoidai masses and 
fibrous crusts coating various rocks over which dilute magnesium sul- 
phate solutions trickle, and mingled with earth 
in the soils of caves The solutions result from 
t k e ac t 10 n upon magnesian rocks of sulphuric 
c,cid derived from oxidumg sulphides Crys- 
tals are rare 

The composition corresponding to MgSOr 
yHkO demands 32,5 SOa, 163 MgO and 51 2 
H 2 

The mineral forms white or colorless bi- 
Ho 142-EpsomitcCrys- sphenoidalj orthorhombic crystals, with an 
tal with OQ P 1 10 (m) , , . -,, 

p axial ratio a b ' c= 9901 i S79 Their 

and -r, in (s) habit is tetragonal The angle no A 1^0=89 

26' The commonest forms occurring on syn- 

P P 

thetic crystals are combinations of ooP(iio), and -T(III) or -~J(ni) 

2 2 

(Fig 142) Natural crystals contain, m addition oo P 56 (oio) and 
POO(IOI) 

The luster of epsomite is vitreous, its hardness 2 0-2 5 and specific 
gravity 170 Its refractive indices for yellow light are a 143 25, 
0=i 4554 and 7= i 48 

The mineral is soluble m water, yielding a solution with a bitter taste 
With a solution of barium chloride it yields a white precipitate of BaSOt 

Epsomite is distinguished from other colorless, soluble minerals by 
its taste and the reactions for S and Mg 

Synthesis Crystals are produced by evaporation of solutions of 
MgSO* containing certain other salts From those containing borax, 
crystals of the type indicated above are separated The production ot 
right or left crystals may be provoked by inoculation of the solution with 
a particle of a crystal of the desired type 

Locakties Epsomite occurs m mineral waters, as, for instance, at 
Seidlitz, Bohemia, on the walls of mines and caves, among the deposits 
of bitter lakes, and as crystals m the soil covering the 'floors of caves 



SULPHATES 251 

Melantente, 01 copperas (FeSO 4 7H 2 0), is usually m fibrous, 
stalactitic or pulverulent masses associated with pynte or other sul- 
phides containing iron, from which it was produced by weathering 
processes It is commonly some shade of green Its streak is colorless 
Its crystals, which are monochmc (prismatic class), are rare The 
mineral has a hardness of 2 and a density of i 9 It is soluble in water, 
forming a solution which has a sweetish astringent taste. 

ALUM GROUP 

The alum group includes a large number of isomorphous compounds 
with the general formula R'A1(S04)2 laHsO The group crystallizes 
in the isometric system (dyakisdodecahedral class), but all of its mem- 
bers are so readily soluble m water that they are rarely found in nature 
The commonest alums are kalmite (KA1 (864)2 I2H20) and soda alum 
(NaAl(S04) 2 



DOUBLE SULPHATES WITH CARBONATES OR CHLORIDES 

A number of compounds of sulphates with chlorides and carbonates 
are known, but of these only one is of any great economic importance 
Two others afford interesting crystals The commercial compound is 
kaimte, which is a hydrated combination of MgS04 and KC1, with 
the formula M&S04 KC1 3H 2 The other two best known members 
of the group are leadhillile (PbSO4 Pb(PbOH)2(COs)2 and hanksite 
(2Na 2 C0 3 QNa 2 S0 4 KCI) 

Kainite (MgSO 4 KCI 3H 2 0) 

Kaimte is found only in beds associated with halite and other deposits 
from saline waters It is rarely crystallized Crystals are monoclmic 
(prismatic class), with a b c=i 2186 : i . 5863 and =85 6'. They 
possess a pyramidal habit with oP(ooi) and dbP(ni)(iiT) predom- 
inating 

The mineral usually forms granular masses which are white, yellow, 
gray or red It is transparent, has a hardness of 2 and sp gr 2.13, 
and is easily soluble in water Its refractive indices for sodium light are- 
01=14948 and 7*1.5203 

When heated in a glass tube it yields water and HC1 It is distin- 
guished from other soluble minerals by this reaction, and by the fact 
that it yields the test for sulphur, and colors the flame blue when its 
powder is mixed with CuO and heated before the blowpipe 



252 DESCRIPTIVE MINERALOGY 

Synthesis Crystals have been produced by evaporating a solution 
of K2S04 and MgSOi containing a great excess of MgCb 

Occurrence Kaimte occurs in the salt beds of Stassfurt, Germany, 
and of Kalusz in Gahcia, and in the deposits of salt lakes and lagoons 
It also occurs as crusts on some of the lavas of Vesuvius 

Uses. The mineral is utilized as a source of potassium m the manu- 
facture of potassium salts and fertilizers Large quantities are imported 
annually into the United States In 1912 the imports aggregated 
485,132 tons, valued at $2,399,761 




Hanksite (2Na2CO3 pNa2SOi KC1) occurs almost exclusively in 

. hexagonal prisms that are prismatic or tabular, 

or in double pyramids suggesting quartz crys- 
tals Their axial ratio is i . i 006 The com- 
monest crystals are bounded by oP(oooi), 
FIG 143 Hanksite Crys- ooP(ioTo), P(ioTi) (Fig. 143) and 2P(202i), 
tal with OOP, joio (w), or |p( 4 o4s) Their cleavage is imperfect 
P, ion (0) and oP, oooi p ^ M ^ o p (oool) Thc mmeml fe wh j te Qr 

yellow Its hardness -2 and its specific 
gravity =256 It is soluble m water. Its refractive indices are 
w=i 4807 and =i 4614 It occurs at Borax Lake and Death Valley, 
California, in the deposits of salt lakes 



LeadhUlite (PbSO 4 Pb(PbOH) 2 (CO,<02) occurs principally as 
crystals m the oxidized zones of lead and silver veins The crys- 
tals are monoclmic (prismatic class), and have an hexagonal habit. 
Their axial ratio is i 7515 11:2 2261. j9=8932'. The principal 
forms observed on them are oP(ooi), oo'P(no), ooP<w (too), P(m) 
and P6o (102) In the most common twins ooP(no) is the twin- 
ning plane The mineral is white or yellow, green or gray, and it is 
transparent or translucent Its streak is colorless It is sectile, has a 
hardness of 2 5 and a specific gravity of 6.35 Before the blowpipe it 
mtumesces, turns yellow, and fuses easily (i 5) Upon cooling it again 
becomes white It effervesces m HNOs and leaves a white precipitate 
of PbS04 It reacts for sulphur and water It is found at Leadhills, 
Scotland, and Mattock, England, associated with other ores of lead; 
at a lead mine near Iglesias, Sardinia, and at several silver-lead mines 
in Arizona. 



CHAPTER XIII 



THE CHROMATES, TUNGSTATES AND MOLYBDATES 

THE CHROMATES 

The only chromate of importance, among minerals, is the lead salt of 
normal chromic acid, HkCrO* There are several other chromates 
known, but they are basic salts and are rare All are lead compounds 
The normal salt, PbCrO*, is known as crocoite Chromic acid is un- 
known, as it spontaneously breaks down into CrOa and water when set 
free from its salts Its best known compound is potassium chromate, 



Crocoite (PbCr0 4 ) 

Crocoite is well characterized by its hyacinth-red color It is a lead 
chromate with PbO=68 9 per cent and 003=31 i per cent. 

Its crystallization is monoclmic 
(prismatic class) with a . b : c 
= 9603 : i . 9159 and 0=77 33'- 
Its crystals, which are usually im- 
planted on the walls of cracks in 
rocks, are prismatic or columnar 
parallel to ooP(no) Their pre- 
dominant forms are ooP(no), 
P(iu), and various domes (Fig 
144). Their* cleavage is distinct 
parallel to ooP(uo) The angle 
1 10 A no=86 19' The mineral 
also occurs in granular masses 

Crocoite is bright hyacinth-red, 
and is translucent Its streak is 
orange-yellow The mineral is sec- 
tile Its fracture is conchoidal, its 
hardness 2.5-3 and density about 6 
is about 2 42, 

In the closed tube it decrepitates, and blackens, but it reassumes its 
red color when heated On charcoal it deflagrates and fuses easily, 

253 




FIG 144 Crocoite Crystals with >P, 
no (m), cop}, 120 (/), -P, in 0), 
3 Po5, 301 (*), PS5, Tor (), oP, 

001 (C), P>,OII (*), 2? CO, 021 (?) 

and iPSb,oi2 (w) 

Its intermediate refractive index 



254 DESCRIPTIVE MINERALOGY 

yielding metallic lead and a lead coating With minocosmic salt it 
gives the green bead of chromium 

The mineral is easily lecogmzed by its color and the test for chro- 
mium 

Synthesis Crystals, like those of crocoite, have been obtained by 
heating on the water bath a solution of lead nitrate in nitric acid and 
adding a dilute solution of potassium bichromate 

Occurrence Crocoite occurs under conditions which suggest that it 
is a product of pneumatolysis 

Locahhes It is found in the Urals, at Rezbanya and Moldawa, m 
Hungary, m Tasmania, and m the Vulture Mining district, Mancopa 
Co , Arizona, 

THE TUNGSTATES AND MOLYBDATES 

The tungstates are salts of tungstic acid, EfoWC^ They are the 
principal sources of the metal tungsten which is beginning to have im- 
portant uses The molybdates are salts of molybdic acid, liaMoOt 
The two most prominent tungstates arc ideditc, CaWQi, and wolf- 
ramite (Fe Mn)W04, and the most prominent molybdate is wulfenite, 
PbMoO* 

All tungsten compounds give a blue bead with salt of phosphorus in 
the reducing flame When fused with NagCOa, dissolved in water 
and hydrochlonc acid, and treated with metallic zinc (see pp 482, and 
492 for details of test), they also yield a blue solution which rapidly 
changes to brown 

The molybdates give with the salt of phosphorus bead in the oxidis- 
ing flc,me a yellow-green color while hot, changing to colorless when cold. 
In the reducing flame the color is clear green. 

SCHEELITE GROUP 

The scheelite group comprises a series of tungstates and molybdates 
of Ca, Cu and Pb The minerals arc tetragonal and hcmihcdral and 
are all well crystallized The more important members of the group 
are scheehte and wulfemte CuprotungMe is a copper tungstate (CuW04) 
and stolzite a lead tungstate 



Scheelite 

The formula of scheelite demands 80 6 per cent WO.?, and 194 per 
cent CaO, but the mineral usually contains a little molybdenum in 
place of some of the tungsten It nearly always contains also a little Fe. 



CHROMATES, TUNGSTATES AND MOLYBDATES 255 

Scheehte crystallizes in the tetragonal bipyraimdal class Its crys- 
tals are usually pyramidal, though often tabular m habit Their axial 
ratio is i : i 5268 On the pyramidal types the predominant planes 
are pyramids of the first, second (Fig 145), and third orders and on the 
tabular types, in addition, the basal plane One of the most familiar 

combinations is P(m),P co (101), y (313) and | ^lj(i 3 i) (Fig 145), 

Other forms frequently found on its crystals are |P oo (102) and P 
(105) The angle no A In = 79 SSi' Twinning is common, both 
contact and penetration twins having oo p oo (100) as the twinning 
plane The mineral aJbO occurs m remform and granular masses 

Scheehte is white, yellow, brown, greenish or reddish, with a white 





FIG 145 FIG 146 

FIG 145 SdiceliLc CryoUl with P, in \pj t P oo , 101 (e) and oP, ooi (c), 
FIG 146 Scheehte Crybtal with 1> and e as in Fig 145 Also I ~ I , 313 (h) and 



streak and vitreous luster It has a distinct cleavage parallel to P(ooi), 
and an uneven fracture It is brittle, has a hardness of 4 3-5 and a 
density of about 6, and is transparent or translucent It is soluble in 
HC1 and HNOs with the production of a yellow powder, tungsten tri- 
oxide, which is soluble m ammonia Its refractive indices are = i 9345, 
w= i 9185 for red light 

Before the blowpipe the mineral fuses to a semitransparent 
glass With borax it forms a transparent glass which becomes opaque 
on cooling With salt of phosphorus it yields the characteristic beads 
for tungsten, but specimens containing iron must be heated with tin on 
charcoal before the blue color can be developed 

Scheehte is distinguished from limestone, which its massive forms 
closely resemble, by its higher specific gravity and the absence of effer- 



256 DESCRIPTIVE MINERALOGY 

vescence with HC1 From quartz it is distinguished by its softness and 
from bante by greater hardness and higher specific gravity 

Syntheses Crystals of scheehte have been made by adding a solu- 
tion of sodium tungstate to a hot acid solution of CaCk, and by fusing 
the two compounds They have also been produced by fusing wolfram- 
ite with CaCl 2 

Occurrence and Origin Scheehte is found m gold-quartz veins 
and in veins cutting acid igneous rocks, where it is associated with 
cassiterite, topaz, fluorite, molybdenite, wolframite and many other 
metallic compounds, and as a contact metamorphic product in altered 
limestone intruded by granite It is probably m all cases a deposit 
from hot solutions 

Localities It occurs at Zinnwald, Bohemia, Altenbeig, Saxony, 
Carrock Fells, Cumberland, England, Pitkaranta, Finland, in New 
Zealand, and in the United States at Monroe and Trumbull, Conn , in 
the Atoha District, Kern Co , California, the Mammoth Mining Dis- 
trict, Nevada, in Lake County, Colorado, near Gage, New Mexico, 
where it occurs with pynte and galena in a vein cutting limestone, 
and in the placer gravels at Nome, Alaska 

Uses of Tungsten Tungsten is used puncipally m the manufacture 
of tool steel, electric furnaces and targets for Ronlgen rays It is 
employed also as filaments m electric-light bulbs, in the manufacture 
of sodium tungstate which is used for fireproofing cloth, as a mordant 
in dyeing, and for a number of other minor purposes 

Production Scheehte has been mined in small quantity m Idaho, 
Alaska, California, Nevada, Arizona, and New Mexico, Us a source of 
tungsten, but most of this element has heretofore been produced from 
other compounds, mainly wolframite In 1913 a few hundred tons of 
scheehte concentrates were produced m the Atoha district, California, 
and the Old Hat district, near Tucson, Ariz. At present (rgi6) it is 
being produced in large quantity near Bishop, Inyo Co., Cal. 

Stolzite (PbWO4) is completely isomorphous with wulfenite. Its 
crystals, which are pyramidal or short columnar, arc mainly combina- 
tions of oP(no), P(in), 2P(22i) and oP(ooi) Their axial ratio is 
i . i 5606 

The mineral is gray, brown, green or red. It is translucent and 
has a white streak Its hardness is 2 75-3 and its sp. gr 7.87-8.23. 
Its refractive indices for yellow light #re- w =2 2685, = 2 182 

Before the blowpipe it decrepitates and melts to a lustrous crystal- 
line globule. The bead with microcosmic salt in the reducing flame 



CHROMATES, TUNGSTATES AND MOLYBDATES 257 

is blue when cold, in the oxidizing flame it is colorless The mineral 
is decomposed by HNOs leaving a yellow residue ol WOs Crystals 
have been made by fusing sodium tungstate and lead chloride 

Its principal localities are the tm-bearing veins at Zmnwald, Bo- 
hemia, the copper veins in Coquimbo, Chile, and Southampton, Mass , 
where it is associated with other lead compounds 

Wulfenite (PbMoO 4 ) 

Wulfemte is the only molybdate of importance that occurs as a 
mineral Its formula demands 39 3 MoOs and 60 7 PbO Calcium 
sometimes replaces a part of the Pb and tungsten a part of the Mo. 

Wulfemte is hemihedral and hemimorphic (tetragonal pyramidal 
class) Its crystals are more frequently tabular than those of scheelite, 
and they are usually very thin 

The mineral, however, occurs also m pyramidal and prismatic crys- 
tals which, in some cases, exhibit distinct hemunorphism Their axial 





Fro 147 FIG 148 

FIG 147 Wulfemte Crystal with o P <*> , 100 (a) and ^P o , i o 12 (0) 

FIG 148 Wulfenite Crystal with oP, ooi (c), JPoo, 102 (), P, 101 (e), 

P, in (M) and JP, 113 (s) 

ratio is a ' c=i . i 5777 The most common forms found on its crys- 

r oo pal 
tals are oP(ooi), P(ni), j 1 (320), fP(ii3) and POO(IOI) (Fig 

147 and 148). The angle in /\1n = So 22'. 

The cleavage, parallel to P, is very smooth, and the fracture is con- 
choidal The mineral is brittle Its hardness is about 3 and specific 
gravity about 6 8 Its luster is resinous or adamantine, and its color 
orange-yellow, olive-green, gray, brown, bright red or colorless Its 
streak is white and it is transparent For red light, o>= 2 402, e= 2 304 

Before the blowpipe wulfenite decrepitates and fuses readily With 
salt of phosphorus it gives the molybdenum beads With soda on 
charcoal it yields a lead globule. When the powdered mineral is evap- 
orated with HC1 molybdic oxide is formed On moistening this with 
water and adding metallic zinc an intense blue color is produced. 

Wulfenite is distinguished from tanadmtte (p 271), by crystalliza- 
tion, by the test for chlorine (vanadimte) and the test for tungsten. 



258 DESCRIPTIVE MINERALOGY 

Synthesis Wulf emte crystals have been produced by melting 
together sodium molybdate and lead chloride 

Occurrence and Localities The mineral occurs in the oxidized zone 
of veins of lead ores at some of the principal lead occurrences in Europe, 
and in the United States near Phoenixville, Pennsylvania, in the Organ 
Mountains, New Mexico, at the mines in Yuma County, Arizona, at 
the Mammoth Mine, m Pmai County in the same State, and at many 
other of the lead mines m the Rocky Mountain states 

Uses Wulfenite is an important source of molybdenum, but, 
because of the few uses to which this metal is put, the amount of wulfen- 
ite mined annually is very small 

WOLFRAMITE GROUP 
Wolframite ((Fe MnJWO*) 

Wolframite is the name given the isomorphous mixtme of the man- 
ganese and iron tungstates that occur neaily puu* in some vanctics 
of the mineials hubnente and fcrbente 

The mixture of the uon and manganese molecules is more common 
than either alone, consequcntl} wolframite is the commonest member of 
the group. The properties of all three mmcials, ho\ve\cr, arc so nearly 
alike that they must be distinguished by chemical analysis 

The name wolframite is usually applied to mixtures of the tungstates 
in which the proportion of Fe to Mn \uries between 4 : i and 2 3, or 
between g 5 per cent and 189 per cent of FeO and 14 pci cent and 
4 7 per cent of Mn02. 

It has recently been suggested that the name ferbente be limited 
to mixtures containing not more than 20 per cent of the hubnente mole- 
cule and the name hubnerite to those containing not more than 20 per 
cent of the ferbente molecule This would leave the name wolframite 
for mixtures containing more than 20 per cent of both FcW04 and 
MnW0 4 

Analyses of specimens of hubnente (I), wolframite (II and III) 
and ferbente (IV) follow 

W0 3 FeO MnO CaO Other Total 

I Ellsworth, Nye Co , Nev 7488 56 2387 .14 16 9961 

II Sierra Cordoba, Argentine 7486 1345 ".2 , 122 10055 

III Cabarrus Co , N C . 7579 1980 5.35 .32 tr 101.26 

IV, Kwnbosan, Japan 75 47 24 33 tr tr 99.80 

All members of the group crystallize m the monoclinic system 
(prismatic class) with axial ratios as follows 



CHROMATES, TUNGSTATES AND MOLYBDATES 259 



Ferbente a . b c= 8229 i 
Wolframite = 8300 i 

Ilubmtite =8315 i 



8463 0=89 38' 
8678 0=89 38' 
8651 0=89 38' 




The crystals are pusmatic or cubic in habit and are bounded by 

ooP(uo), ooPooJioo), and two 01 more of the following oP(ooi), 

oo P .56 (oio), oo P 2 (2io), P oo (on), -]P 66 (To2), - JP 66 (102), -P(in), 

- 2?2(i2i) and +2P oo (102) (Fig 149) The 

angle iioAiio for ferbente = 78 51', for wol 

frcimite 79 23', and foi hubnente 79 29' 

Twins are fairly common, with oo P 66 (100) 

the twinning plane Cleavage is perfect 

parallel to oo P 03 (oio) The minerals also 

occur m lamellar and granular masses 

Hubnente is brownish red to black and 
translucent, wolframite is black and trans- 
lucent only on thin edges, and ferbente is ^'49 -Wolframite Crys- 
, . . / * ' . .. tal with oop, no ( m ), 

black and opaque. The streak is yellow to oopj, 2 io (/) oopoo 

yellowish brown in hubnente and brown or 100(0), JPoo, 102 (/), 
brownish black in ferbente, with the streak P, 011 (/), 2Fa,iai 
of wolframite between W> +i p55 > i* (y) and 

Wolframite is buttle, has a hardness ot ~~ P> IIX W 
5-5 5, a specific gravity of 72-75, and a submetallic luster Before 
the blowpipe it fuses to a globule which is magnetic Fused with 
soda and niter on platinum it gives the bluish green manganate. The 
salt of phosphorus bead is reddish yellow when hot and a paler tint 
when cold. In the reducing flame the bead becomes dark red If 
the mineral is treated first on charcoal with tin its bead assumes a 
green color on cooling. The mineral dissolves in aqua regia with 
the production of the yellow tungsten trioxide When treated with 
concentrated HgSOi and zinc it yields the blue tungsten reaction 

Crystals of wolfiamite are easily distinguished from crystallized 
colnmbiie (p 293), samarskite (p. 295), and uraninite (p 297), by dif- 
ferences in crystallization Massive wolframite is distinguished from 
massive forms of the other three minerals by its more perfect cleavage 
and by the reactions with the beads Uranmite, moreover, contains 
lead Wolframite is distinguished from black tourmahne (p. 434) by 
the differences m specific gravity, 

Occurrence and Ongin Wolframite usually occurs in veins with tin 
ores, and in quartz veins with various sulphides, and in pegmatite. 
Its origin is probably pneumatolytic. 



260 DESCRIPTIVE MINERALOGY 

Localities Wolframite is found m all tm-producmg districts, espe- 
cially at Zmnwald, Schneeberg and Freiberg, in Germany, at Ner- 
chinsk, in Siberia, m Cornwall, England, at Oruro, in Bolivia, and at 
various points in New South Wales, Australia 

In the United States it occurs at Monroe, Conn , near Mine La 
Motte, Missouri, near Lead, South Dakota, where it impregnates a 
sandy dolomite, and at Hill City in the same State in quartz veins, 
sometimes containing cassitente, in Boulder Co , Colorado, in veins 
m granite (ferbente), neai Butte, Montana, in quaitz veins carry- 
ing silver ores (hubnente), and the quartz-cassitcnte veins near Nome 
and on Bonanza Creek, in Alaska, and in quarts veins at various 
points in Washington, Idaho, California, Nevada, New Mexico and 
Arizona At some of these localities the mineral is more properly 
hubnente 

One or another of the three has been mined in Colorado, Nevada, 
South Dakota, Montana, Washington, Calif oinu, Aiizona, and New 
Mexico, but the total production has never been laige Some of the 
ore shipped has been obtained from placers along streams that dram 
regions containing the mineral m veins, but most of it has been obtained 
from vein rock which is crushed and concentrated 

Uses These three minerals constitute the principal source of tung- 
sten used in the arts The uses of the metal are referred to under 
scheehte 

Production The total production of concentrates containing 60 
per cent WOs in the United States during 1913 was 1,325 tons, valued 
at $640,500. Of this, 953 tons were ferberite from Boulder Co., 
Colorado A little hubnente was produced in the Arivica region, m 
southeast California, at Dragoon, Arizona, at Round Mountain, Nevada, 
and on Paterson Creek, Idaho. In addition, there were imported 
$86,000 worth of tungsten-beaimg ores and $143,800 worth of tung- 
sten metal and ferro-tungsten. The world's production of tungsten ore 
in 1912 was 9,115 tons. 



CHAPTER XIV 
THE PHOSPHATES, ARSENATES AND VANADATES 



THE phosphates are salts of phosphoric acid, HsPO^ the arsenates 
of the corresponding arsenic acid, HsAsO^ and the vanadates of the 
corresponding vanadic acid, HaVC^ The phosphates are by far the 
most important as minerals They are easily distinguished by yielding 
phosphme, HsP, upon igniting with metallic magnesium and moistening 
the resulting Mg 3 P 2 with H 2 or HC1 (Mg 3 P2+6HCl=3MgCl 2 + 
2PHs) The gas is recognized by its disagreeable odor The arsenates 
are detected by the test for arsenic 

The arsenates, phosphates and vanadates form groups of isomor- 
phous compounds, the most important of which is the apatite group 
Those occurring as minerals are divisible into several subgroups, of 
which the following six contain common minerals, viz (i) anhydrous 
(a) normal salts, (V) basic salts and (c) acid salts, and (2) hydrous 
(a) normal salts, (b) basic salts and (c) acid salts 

A number of the phosphates and arsenates are of value commercially 
either because of the phosphorus they contain, because they are sources 
of valuable metallic salts, because they serve to indicate the presence 
of other valuable compounds, or because they possess an ornamental 
character 

Nearly ail the phosphates are transparent or translucent and all are 
nonconductors of electricity or are very poor conductors, 

ANHYDROUS PHOSPHATES, ARSENATES AND 
VANADATES 

NORMAL PHOSPHATES, ARSENATES AND VANADATES 

The minerals belonging in this class of compounds are not as numer- 
ous as the basic salts, but some of them are of great value The class 
includes phosphates of yttrium, the alkalies, beryllium, cerium, mag- 
nesium, iron and manganese and a group of isomorphous phosphates, 
arsenates and vanadates -the apatite group in which a haloid radicle 
replaces one of the hydrogen atoms of the acids Apatite, the prin- 
cipal member of the group, is an important source of phosphoric acid 

261 



262 DESCRIPTIVE MINERALOGY 

Triphylite (Li(Mn Fe)PO 4 ) Littuophilite 

Triphylite is the name usually applied to the isomorphous mixture 
of LiFeP04 and LiMnP04, m \vhich the manganese molecule is present 
in small quantity only The mixture containing a large excess of the 
manganese molecule is called lithiophihte 

The pure tnphyhte molecule contains FeO=45 5 P er cent, LigO 
= 9 5 per cent and P2Ch=45 per cent The pure lithiophilite molecule 
consists of 45 i per cent MnO, 9 6 per cent Li 2 and 45 3 per cent 

P 2 5 

Both substances are orthorhombic (bipyramidal class), with an axial 
ratio approximating 4348 " i : 5265 Crystals are rare and not well 
developed They are usually rough prisms bounded by ooFoo (oio), 
oP(ooi), ooP(no), ooP2(i2o) and 2Po6 (021) The minerals usually 
occur massive, or in irregular, rounded crystals, with two very dis- 
tinct cleavages 

Both minerals are transparent to translucent, both have a white 
streak, and both are vitreous to resinous in lustci Thou baldness is 
about 4 5-5 and sp gr about 3 5 Triphylite is greenish gray to blue, 
and lithiophilite pink, yellow or brown The refi active indices for 
light brown lithiophihte are a=i 676, j3=i 679, 7=1 687, those for 
blue triphyhte are a trifle higher 

When heated in closed tubes both compounds are apt to turn dark 
They fuse at a low temperature (i 5) and color the flame crimson In 
the case of tnphyhte the crimson streak is bordered by the green of iron. 
Lithiophilite gives the reactions for Mn Most specimens give reac- 
tions for all these metals Fe, Mn and Li Both minerals are soluble 
inHCl 

The two minerals are distinguished from other compounds by their 
reactions for phosphorus and lithium, and from each other by the reac- 
tions for Fe and Mn 

Occurrence They usually occur as primary constituents of coarse 
granite veins They are associated with beryl, tourmaline and other 
pneumatolytic minerals and with secondary phosphates, which are 
presumably weathering products of the pnmary phosphates 

Locahties Both minerals occur at a number of points associated 
with other lithium compounds, especially spodumene (p 378) In this 
country tnphylite has been found at Peru, Maine, Grafton, Ne\\ 
Hampshire, and Norwich, Massachusetts, lithiophihte at Branchville, 
Connecticut, and at Norway, Maine 

Neither of the minerals possesses a commercial value at present. 



PHOSPHATES, ARSENATES AND VANADATES 263 



Beryllonite (NaBeP0 4 ) 

Beryllomte is a comparatively rare mineral occurring at only a few 
places and al\\ t iys in crystals or in crystalline grams 

Its composition is 24 4 per cent Na^O, 19 7 per cent BeO and 55 9 
per cent P2Cb 

Its crystals are orthorhombic (bipyramidal class), with an axial 
ratio 5724 i * 540 They are short pyramidal or tabular in habit, 
often exhibiting a pseudohexagonal symmetry. Most crystals are 
highly modified with oP(ooi), oo P 60 (100), oo P 66 (oio), P 66 (101) 
and 2P?(i2i), the principal forms Twins are common, with oo P(no) 
the twinning plane The crystal faces are frequently strongly etched 

The mineral is white to pale yellow It has a vitreous luster, 
except on oP(ooi), where the luster is sometimes pearly It possesses 
four cleavages, of which the most perfect is parallel to oP(ooi). That 
parallel to oo P 60 (100) is distinct, but the others are indistinct Its 
hardness is 5 5-6 and its density 2 845 Its fracture is conchoidal 
Crystals often contain numerous inclusions of water and liquid C02 
arranged in lines parallel to L Its refractive indices for yellow light 
are a=i 5520, jS=i 5579, 7=1 5608 

Beiyllomte decrepitates and fuses in the blowpipe flame to a cloudy 
glass, at the same time imparting to the flame a yellow color It is 
slowly soluble in HC1, and gives the phosphorus reaction with mag- 
nesium 

It is distinguished from most other colorless transparent minerals 
by the reaction for phosphorus, from other colorless phosphates by its 
crystallization and the sodium flame test 

Occurrence and Localities The best known occurrence of beryllo- 
nite m the United States is Stoneham, Maine, where it is found in the 
debris of a pegmatite dike associated with apatite (p 266), beryl (p. 359), 
and other common constituents of pegmatites It originally existed 
implanted on the walls of cavities in the pegmatite and was apparently 
the result of pneumatolytic processes 

Use. The mineral is used to some extent as a gem stone, 

Monazite ((Ce Di La)PO 4 ) 

Monazite is the principal source of certain rare earths that are used 
m manufacturing gas mantles Although it occurs as small grams and 
crystals m certain granites it is found m commercial quantities only m 
the sands of streams. 



264 DESCRIPTIVE MINERALOGY 

The mineral is a phosphate of the metals cerium, lanthanum, praseo- 
didymium and neodidymium in most cases combined with the silicate of 
thorium Its composition may be represented by the formula 

*((Cc La Di)P0 4 )+^(ThSi0 4 ), 

in which the proportion of the second constituent varies from a trace to 
an amount yielding 20 per cent ThC>2 Since this is not constant in 
quantity it is not to be regarded as an essential portion pf the com- 
pound It is probable that in monazite we have to do with a solid 
solution of cerium and thorium phosphates, thorium silicate and oxides 
of the rare metals 

Monazite is monochnic with a b : c= 9693 ' i : 9255 and 0= 
76 20' Crystals are usually prismatic with the pinacoids oo P 56 (100), 
ooPob(oio), the prism ooP(no), the two domes POO(IOI) and 
+P66(ioY) and the pyramids -P(in) and +P(nT) They are 
often flattened parallel to the orthopmacoid 
(Fig 150) The angle 1 10 A iTo= 86 34' 

Their cleavage is perfect parallel to oP 
The color of the mineral is gray, yellow, red- 
dish, brown or green It is usually transpar- 
ent or translucent and sometimes opaque It 
is brittle, has a white streak, and a resmous 
luster Its hardness is 5-5 5 and its sp gr 
FIG. 150 Monazite Ciys- 4 7-5 3, varying with the proportion of thorium 
tal with oo POO, ioo (a), nt The re f ra ctive indices for yellow 

00 P. 110 (0Z), 00 ?2, , , 

o (,), oo P S, oxo (*), h S ht are a=I 7938, 7 - t 8 45 2. 
-Poo, ioi (w), +Pco, The mineral is infusible Before the blow- 
iol (x) and P, nI () pipe it turns gray, and when moistened with 
H2S04 it colors the flame bluish green It is 

difficultly soluble in HC1 and HNOs Most specimens are strongly 
radioactive 

Synthesis Crystals of monazite have not been prepared, but crys- 
tals of cerium phosphate similar to those of monazite have been made 
by heating to redness a mixture of cerium phosphate and cerium chloride 
Occurrence and Ongvn Monazite occurs as the constituent of cer- 
tain granites and granitic schists in small crystals scattered among the 
other components In this form it is a separation from the granitic 
magma When the granites are broken down to sand by weathering 
the monazite is freed and because of its specific gravity it concentrates 
in stream channels 

Localities Although the mineral is fairly widespread in the rocks, 




PHOSPHATES, ARSENATES AND VANADATES 265 



it is concentrated into commercial deposits at only a few places. The 
most important of these are in southeastern Brazil, in Norway, and in a 
belt 20 to 30 miles wide and 150 miles long extending along the east side 
of the Appalachian Mountains from North Carolina into South Carolina 

The mineral has also been reported from many points in ten coun- 
ties in Idaho Near Centerville it may be m sufficient quantity to be 
of commercial importance 

Preparation Monazitg is separated from the valueless sand in 
which it is found, by washing, and the residues thus resulting are further 
concentrated by a magnetic process The commercial concentrates 
produced in this way usually contain from 3 to 9 per cent ThCfe, and 
their price varies accordingly 

Production and Uses Monazite is the chief source of thorium oxide 
used in the manufacture of incandescent gas mantles Formerly it was 
produced in large quantity in the Carohnas, the production m 1909 
amounting to 542,000 Ib , valued at $65,032, and in 1905 to 
1,352,418 Ib , valued at $163,908. All of this was manufactured into 
the nitrate of thorium in this country and the amount made was 
not sufficient to meet the domestic demand. Consequently, large quan- 
tities of the nitrate were imported In 1910-11 mining of the mineral 
m the Carohnas ceased and all the monazite needed has been imported 
since then The imports of thorium nitrate for 1912 were 117,485 Ib , 
valued at $225,386 and of monazite, an amount valued at $47,334 

Xenotime (YPO 4 ) 

Xenotime, though essentially an yttrium phosphate, usually contains 
erbium and in some cases cerium. 
It occurs in tetragonal crystals 
and m rolled grains Its axid 
ratio is i 6177 an d ^ e angle 
in A ill =* 55 30' Its crystals 
are octahedral or prismatic and 
are bounded by oo P(iio),P(m), 
and in some cases by oo P oo (100) 
and 2P oo (201) (Fig 151) Their 
cleavage is perfect parallel to FIG 151 -Xenotime Crystals with OOP no 

n/ \ onT iv W P II3C W ^ ^P 00 * I W 

ooP(no) The mineral is brown, v " 

pink, gray or yellow Its streak is a pale shade of the same color. 
It is opaque and brittle Its luster is vitreous or resinous, its hardness 
4-5 and specific gravity 45 Its indices of refraction are: e=i8i, 
w=i 72 




266 DESCRIPTIVE MINERALOGY 

Xenotime is infusible, insoluble in acids and with difficulty soluble 
in molten microcosmic salt It is distinguished from zircon by its 
cleavage and inferior hardness 

A variety of xenotime containing a small percentage of sulphates is 
known as hussakite 

The mineral occurs in pegmatite veins, in granites and in the sands 
of streams It is found in pegmatite veins at Hittero, Moss, and other 
places in Norway, at Ytterby, Sweden, in the granites of Mmas Geraes, 
Brazil, and m the gold washings at Clarksville, Georgia, and many places 
in North Carolina, and in pegmatite veins in Alexander County in the 
same State 

APATITE GROUP 

The apatite group consists of a number of phosphates, arsenates and 
vanadates in which fluorine or chlorine takes the place of the hydroxyl 
in basic compounds Thus, fluorapatite is Ca4(CaF)(P04)s and chlor- 
apatite Ca^CaGXPOOs The group contains a number of important 
minerals, of which apatite is by far the most valuable These minerals 
are isomorphous, all crystallizing in the hemihedral division of the hex- 
agonal system (hexagonal bipyramidal class) The names, composi- 
tions and axial ratios of the most important are as follows 

Fluorapatite Ca4(CaF)(PC>4)3 a c=i 7346 

Chlorapatite Ca^CaClXPCWs a c**i: 7346+ 

PyromorpTtite Pb4(PbCl)(P04)3 a.c=i 7293 

Mimetite Pb 4 (PbCl)(As0 4 )3 . e-i : 7315 

Vanadmite Pb4(PbCl)(V04)s a:c-i: 7122 



Apatite (Ca4(Ca(F C1))(PO 4 )3) 

Although fluorapatite and chlorapatite are distinct compounds with 
slightly different properties, nevertheless, because of the difficulty of 
discriminating between them without analyses, the name apatite is 
commonly applied to both This is justified because of the fact that the 
two compounds are completely isomorphous, and the mineral as it 
usually occurs is a iruxture, of both The ideal molecules comprising 
the two varieties of apatite have the following compositions 



Fluorapatite CaO=5S5, F=3 8, P 2 5 =42 3 
Chlorapatite CaO=53 8, Cl=6 8, P20s==4i o 



Apatite is found in well defined crystals, sometimes very large 
These have a holohedral habit, but etch figures on their basal planes 



PHOSPHATES, ARSENATES AND VANADATES 267 



reveal the grade of symmetry of pyramidal hemihednsm The min- 
eral occurs also massive, in granular and fibrous aggregates and less 
commonly in globular forms and as crusts 

The crystals are usually columnar or tabular, with the hexagonal 
prism or pyramid well developed Although in some cases highly 
modified, most crystals contain only the oo P(iolo), P(ioTi) and oP(oooi) 
planes prominent, though P(iol2) and 2P2(ii2i) are not uncommon as 
small faces (Figs 152 and 153) Their cleavage is indistinct, and their 
fracture often conchoidal 

Apatite may possess almost any color In a few cases the mineral is 
colorless or amethystine and transparent, but in most cases it is trans- 
lucent or opaque and white, green, bluish, brown or red Its streak is 





FIG 152. FIG 153 

FIG 152 Apatite Crystals with cop, ioYo (w), P, loTi (r), oP, oooi (c), JP, 

iol2 (r) and oop2, 1120 (a) 

FIG 153 Apatite Crystal with m, %, r and c as in Fig 152 and 2?, 2021 (y), 4P|, 
1341 (), 3?J, 1231 GU), 2P2, nil (5), P2, 1122 (B) and oo?}, 1230 (A) 

white and its luster vitreous to resinous Its hardness is 4 5-5 and sp 
gr between 3 09 and 3 39 The refractive indices of fluorapatite for 
yellow light are 6>=i 6335, =1.6316 and of chlorapatite, co=i 6667 
Many specimens are distinctly phosphorescent Nearly all fluoresce in 
yellowish green tints, and all are thermo-electric 

Apatite fuses with difficulty, tinging the flame reddish yellow The 
chlorapatite melts at 1530 and the fluorine variety at 1650 When 
moistened with H2S04 all varieties color the flame pale bluish green, 
due to the phosphoric acid Specimens containing chlorine give the 
brilliant blue color to the flame when fused in a bead of microcosmic 
salt that has been saturated with copper oxide Specimens containing 
fluorine etch glass when fused with this salt in an open glass tube 
The mineral also yields phosphme when ignited with magnesium, and 
it dissolves in HC1 and HNOs 



268 DESCRIPTIVE MINERALOGY 

Apatite is much softer than beryl (p 359)> which it closely resembles 
in appearance It is distinguished from calcite by lack of effervescence 
with acids and from other compounds by the phosphorus reaction 

The vaneties of the mineral recognized by distinct names are 

Ordinary apatite^ crystals or granular masses 

Manganapatite, in which manganese partly replaces the Ca of ordi- 
nary apatite^ This is dark bluish green 

Fibrous, conci etionary apatite Known also as phosphorite 

Osteohte The earthy variety 

Phosphate rock. A mixture of apatite, phosphorite, several hydrous 
carbonates and phosphates of calcium, and fragments of bone and 
teeth It is more properly a rock with a brecciated and concretionary 
structure The composition of typical deposits is represented by the 
following analysis of hard rock phosphate from South Carolina 

CaO P 2 5 C0 2 Fe 2 3 Al 2 0s MgO Insol Undet H 2 Moist 
50 08 38 84 65 96 3 07 30 49 2 46 2 96 07 

Guano is a mixture of various phosphates, both hydrous and an- 
hydrous, calcite and a number of other compounds It is rather a rock 
than a mineral, as it has no definite composition 

Syntheses Crystals of fluorapatite have been made by fusing 
sodium phosphate with CaF 2 and by heating calcium phosphate with a 
mixture of KF and KC1 

Origin The crystallized apatite was formed by direct separation 
from igneous rock magmas and by pneumatolytic action upon limestone 
The phosphorite variety and the phosphate in phosphate rock were 
probably produced by the solution of calcium phosphate and its later 
deposition from solution the original phosphate having been furnished 
in many cases by the shells of mollusca, and by the action of phosphoric 
acid produced by the decay of organisms upon limestone In many 
cases phosphorite accumulated as a residual deposit in consequence of 
the solution of the calcite and dolomite from phosphatic limestone, 
leaving the less soluble phosphate as a mantle on the surface. 

Occurrence The mineral occurs in microscopic crystals as a com- 
ponent of many rocks, as large crystals in metamorphosed limestones, 
as a component of many coarse-grained veins, especially those composed 
of coarse granite and those in which cassiterite, magnetite, tourmaline, 
and other pneumatolytic minerals are found At a number of places 
aggregates of apatite and magnetite or ilmemte occur in such large 
masses as to be worthy of being called rocks An impure apatite in 
concretionary and fibrous forms also occurs in thin beds covering large 



PHOSPHATES, ARSENATES AND VANADATES 269 

areas. It is often mixed with other phosphates, with the bones and 
teeth of animals and with other impurities This is the well known 
phosphate rock or phosphonte 

Localities Crystallized apatite is so widely spread that it is useless 
to mention its occurrences It is mined at Kragero and near Bamle, 
in Norway, at various points in Ottawa County in Quebec, and in 
Frontenac, Lanark and Leeds Counties in Ontario, and at Mineville, 
New York Rock phosphate is found in extensive beds on the west 
side of the peninsula of Florida, in South Carolina, North Carolina, 
Alabama, Tennessee, Wyoming, Idaho, Utah and Arkansas A mixture 
of apatite and ilmemte (nelsomte), occurs as dikes in Nelson and 
Roanoke Counties, Virginia 

Uses The principal use of apatite and phosphate rock is in the 
manufacture of fertilizers The rock (or crushed apatite) is treated 
with H2S04 to make an acid phosphate which is soluble in water Am- 
monia or potash, or both, are added to the mass and the compound is 
sold as a superphosphate. The purest varieties are treated with H2S04 
in sufficient quantity to entirely decompose them, CaSO* and HsPO* 
being formed The latter is drawn off and mixed with additional high- 
grade rock and the mixture is known as concentrated phosphate Super- 
phosphates are manufactured in large quantities in the United States 
and the concentrated phosphates in Europe Unfortunately, for the 
latter use the best grades of apatite or rock phosphate are required, and 
consequently the best grades of rock produced in the United States are 
exported and thus lost to American farmers 

Production The world's production of apatite and phosphate rock 
during 1912 was as follows* 

United States 3,020,905 tons, valued at $11,675,774 

Tunis 2,050,200 tons, valued at 7,500,000 

Christmas Island 159459 tons, valued at 2,024,036 

France 313*151 tons, valued at 1,169,400 

Algeria 207,111 tons, valued at 759455 

Belgium 203,1 10 tons, valued at 316,703 

Other countries 65,000 tons, valued at 280,000 

For the United States production of 1912 the statistics are: 

Florida 2,407,000 tons, valued at $9,461,000 

Tennessee 423,300 tons, valued at 1,640,500 

South Carolina 131,500 tons, valued at 524,700 

Other States 11,600 tons, valued at 49 200 



270 DESCRIPTIVE MINERALOGY 

The total production was 3,020,905 tons, valued at $11,675,77400, 
of which 1,206,520 tons, valued at $8,996,45600 were exported Par- 
tially offsetting this, there were imported guano, apatite and other phos- 
phates to the value of about $2,000 ooo, 

Pyromorphite (Pb 4 (PbCl)(PO 4 )3) 

In composition pyromorphite is PbO, 82 2 per cent, PoOi, 15 7 per 
cent and Cl, 2 6 per cent, but there are usually present also CaO and 



The mineral is completely isomorphous \\ith apatite Its crystals 
are smaller and simpler than those of apatite, but they have the same 
habit Their axial ratio is a c=i ' 7293 This increases to i : 7354 
in varieties containing calcium 

Crystals are often rounded into barrel-shaped forms, and frequently 
are mere skeletons Tapering groups of slender crystals in parallel 
growths are also common Their cleavage is parallel to the &o P(no) 
faces, and their fracture is feebly conchoidal. The mineral also occurs 
in globular, granular and fibrous masses 

Pyromorphite is translucent It is brittle, has a hardness of 3 5-4 
and a density of about 7 Its luster is resinous and color usually green, 
yellow, brown or orange Some varieties are gray or milk-white Its 
streak is white Its refractive indices foi yellow light are: o>=2 0614, 
6=2 0494 The mineral is distinctly thermo-electric. 

When heated m the closed tube pyromorphite gives a white subli- 
mate of lead chloride It fuses easily, coloring the flame bluish green 
When heated on charcoal it melts to a globule, which crystallizes on 
cooling and yields a coating which is yellow (PbO) near the assay and 
white (PbCk), at a greater distance from it. When fused with Na2COs 
on charcoal a globule of lead results The mineral also gives the Cl and 
P reactions The mineral is soluble in HNOa 

Pyromorphite is recognized by its form, high specific gravity and its 
action when heated on charcoal 

Synthesis. Crystals have been obtained by fusing sodium phosphate 
with PbCk. 

Occurrence The mineral occurs principally m veins with other lead 
ores, especially in the zone of weathering It also exists in pseudomorphs 
after galena. 

Localities It is found in all lead-producing regions, especially in 
the upper portions of veins It occurs m particularly good specimens 
at Pribram, Bohemia, at Ems, m Nassau, in Cornwall, Devon, Derby- 



PHOSPHATES, ARSENATES AND VANADATES 271 

shire and Cumberland, England, at Phoemwille, Pennsylvania, and 
at various other points in the Appalachian region 

Vies Pyromorphite alone possesses no commercial value, but it 
is mined with other compounds of lead as an ore of this metal 

Munetite (Pb 4 (PbCl)(AsO 4 )3) 

Mimetite, or mimetesite, resembles pyromorphite in its crystals and 
general appearance, and many of its properties Its color, however, is 
lighter and its density slightly greater It occurs in crystals, m fila- 
ments, and in concretionary masses and crusts Its axial ratio Is 
i 7315 and its refractive indices for yellow light are w=2 1443, e 
= 2 1286 

The formula for mimetite demands 74 9 per cent PbO, 23 2 per cent 
AS205 and 2 4 Cl Usually a portion of the lead is replaced by CaO and 
a portion of the As by P 

Mimetite fuses more easily than pyromorphite It differs from this 
mineral in yielding arsenical fumes when heated on charcoal More- 
over, when heated in a closed tube with a fragment of charcoal it coats 
the walls of the tube with metallic arsenic 

Occurrence and Localities It occurs with other lead minerals in 
veins, usually coating them either as crusts or as a series of small crys- 
tals It is found at Phoenix ville, Pennsylvania, m Cornwall, England, 
at Johanngeorgenstadt, in Germany, at Nerchinsk, Siberia, at Lang- 
ban, in Sweden, and at a number of other places It is, however, not 
as common as the corresponding phosphorus compound 

Uses It is mined with other compounds as an ore of lead. 

Vanadiaite (Pb 4 (PbCl)(VO 4 ))3 

Vanadmite is the most widely distributed of all the vanadium min- 
erals It usually occurs in small bright red prismatic crystals implanted 
on other minerals, or on the walls of crevices in rocks It is one of the 
sources of vanadium 

Its theoretical composition is as follows PbO =78 7 per cent, 
205=19 4 per cent and Cl=2 5 per cent, but phosphorus and arsenic 
are often also present When arsenic and vanadium are present m 
nearly equal quantities the mineral is known as endhckite. 

Its crystals are hexagonal prisms and pyramids bounded by 
ooP(ioTo), oP(oooi), ooP2(u5o\ P(ioTi) and other forms, with an 
axial ratio i : .7122 (Fig 154). Often the crystals have hollow faces 



272 



DESCRIPTIVE MINERALOGY 



(Fig I S5) Frequently they are grouped into pyramids like those of 
pyromorphite The mineral occurs also m globules and crusts 

Vanadmite is brittle, has a hardness of about 3 and a specific gravity 
of about 7 Its fracture is conchoidal Its luster is adamantine or 
resinous and its color ruby red, brownish yellow or reddish brown 
Its streak is white or light yellow The mineral is translucent 
or opaque Its refractive indices for yellow light are ^=2354, 
= 2 299 

In the closed tube vanadimte decrepitates It fuses easily on char- 
coal to a black lustrous mass which is reduced on being further heated 
in the reducing flame to a globule of lead A white sublimate of PbCk 
also coats the charcoal The mineral, moreover, gives the flame test 




FIG. 154 



FIG 154 FIG 155 

Vanadimte Crystal with <x>p, loTo (m), oP, oooi (c), P, icTi (#), and 



FIG 155 Skeleton Crystal of Vanadimte 



for chlorine with copper After complete oxidation of the lead by heat- 
ing in the oxidizing flame on charcoal the residue gives an emerald-green 
bead in the reducing flame with microcosmic salt and this turns to a 
light yellow m the oxidizing flame The mineral is soluble m hydro- 
chloric acid. If to the solution a little hydrogen peroxide is added it 
will turn brown The addition of metallic tin to this will cause it to 
turn blue, green and lavender in succession, in consequence of the reduc- 
tion of the vanadium compounds 

Vanadimte is easily distinguished from most other minerals by its 
color, It is distinguished from other compounds of the same color by 
its crystallization and by the reactions for vanadium 

Occurrence Vanadmlte occurs principally in regions of volcanic 
rocks It is probably a result of pneumatolytic processes 

Localities Crystals are found at Zimapan, Mexico, Wanlockhead, 



PHOSPHATES, ARSENATES AND VANADATES 273 

England, Undenas, Sweden, in the Sierra de Cordoba, Argentine, and in 
the mining districts of Arizona and New Mexico 

Uses Vanadmite is an important source of vanadium, which is 
employed m the manufacture of certain grades of steel and bronze 
Its compounds are, moreover, used as pigments and mordants Most 
of the vanadium compounds produced in this country are obtained from 
other vanadium minerals, among them patromte a mixture, of which 
the principal component is a sulphide (VS.*) and carnotite (p 290), 
but vanadmite has been used abroad and also to a small extent in the 
United States 

WAGNERITE GROUP 

This group, in chemical composition, is analogous to the apatite 
group It includes a number of phosphates and arsenates containing a 
fluoride radical The group is monochmc (prismatic class), with an 
axial ratio which is approximately 19.1 15, with 18=71 50' None 
of its members are important The two most common ones are wag- 
nente (Mg(MgF)PO 4 ), and tnphte (Fe Mn) ((Fe Mn)F)P0 4 

Wagnerite occurs in massive forms and in large rough crystals, with 
imperfect cleavages parallel to oo P 55 (100) and oo P(no) Its crystals 
have an axial ratio of i 9145 i . i 5059 \vith =71 53' They are 
often very complex The mineral is bnttle Its fracture is uneven 
Its hardness is 5 5 and density 3 09 Its color is yellow, gray, pink or 
green It is vitreous, translucent and has a white streak Its refractive 
indices are a=i 569, =i 570, 7 = 1 582 It fuses to a greenish gray 
glass and gives the usual reactions for fluorine and phosphoric acid It 
is soluble in HC1 and HNOa, and heated with HgSOi it yields hydro- 
fluoric acid It occurs in good crystals near Werfen, Austria, and in 
coarse crystals near Bamle, Norway. 

Triplite is an isomorphous mixture of Fe(FeF)PO4 and Mn(MnF)P04 
It usually occurs massive, but is found in a few places in rough crystals 
The mineral is dark brown or nearly black, is translucent to opaque, 
and has a yellowish gra}' or brown streak It possesses two unequal 
cleavages perpendicular to one another and a weakly conchoidal frac- 
ture Its hardness is 4-5 5 and specific gravity about 3 9 Its luster is 
resinous. Its intermediate refractive index is i 660 

Before the blowpipe tnplite fuses easily (i 5) to a black magnetic 
globule It reacts for Mn, Fe, F, and PaOs It is soluble in HC1 and 
evolves hydrofluoric acid with H2S04 It is found in coarse granite 



274 DESCRIPTIVE MINERALOGY 

veins at Limoges, France, Helsingfors, Finland, Stoneham, Maine, 
and Branchville, Connecticut In all of its occurrences it appears to 
be pneumatolytic 

BASIC PHOSPHATES AND ARSENATES 

The basic phosphates are those in which there is more metal present 
than sufficient to replace the three hydrogen atoms in the normal acid, 
HsP04 This is due to the replacement of one or more of the hydrogen 
atoms by a group of atoms consisting of a metal and hydroxyl (OH) 
All yield water when heated in the closed tube 

The principal basic phosphates are amblygonite, a source of lithium 
compounds, dufremte and lazidite, neither of which is of economic im- 
portance, and hbethemte, a copper compound which occurs in compara- 
tively small quantities with other copper ores, and is mined with 
them 

Ohvenite is a basic copper arsenate corresponding to the phosphate 
hbethemte 

Amblygonite (Li(Al(F OH))PO 4 ) 

Amblygomte is an isomorphous mixture of the two compounds 
(AlF)LiP04 and (AlOH)LiPO-i It is an important source of lithium 

The composition of the fluorine molecule is Al20s=344 per cent, 
Li02=io i per cent and P20s=47 9 per cent, making a total of 105 3 
per cent from which deducting 5 3 per cent (0= sF), leaves 100 Nearly 
always a portion of the F is replaced by OH and a part of the Li 
by Na The pure Na(A10H)P04 is known as fremontite, and the pure 
Li(A10H)PO4 as montebrmte 

The analysis of a specimen from Pala, California, gave: 

Pa0 6 AlsOs PesOs MnO MgO LiaO NaaO H 8 O 0-P Total 

4883 3370 12 09 31 988 14 595 229*10131-96 - 100 45 

The mineral forms large, ill-defined triclmic crystals (Fig 156), and 
compact masses with a columnar cleavage Crystals are very rare, and 
are poorly developed Their axial ratio is .7334 : i : 7633. The 
cleavage pieces often show polysynthetic twinning lamellae parallel to 



The cleavage of the mineral is perfect parallel to oP(ooi) Its 
fracture is uneven It is brittle, has a hardness of 6 and a density of 
3 03, Its color is white, gray, or a very light tint of blue, pink or 
yellow Its luster is vitreous, except on oP where it is pearly. ' Its 



PHOSPHATES, ARSENATES AND VANADATES 275 




FIG 156 Amblygoiute 
Crystal with ooPoo, 
100 (a), oP, ooi (c), 
oo ]P, no (A/), oP', 
no (m) y w'P's, 120 

(=), /P/J5, ioi (K) 

and 2'P oo , 02 1 (e) 



streak is white and it is translucent Its refractive indices for yellow 
light are a=i 579, /3=i 593, 7=1 597 

In the closed tube at high temperature it yields water which reacts 
acid and corrodes glass It fuses easily to an 
opaque white enamel It colors the flame red 
with a slight fringe of green When moistened 
with H2S04 it tinges the flame bluish green 
When finely powdered it dissolves readily in 
H 2 SO4 and with difficulty in HC1 

Amblygomte resembles in appearance many 
other minerals, especially spodumene (p 378), 
and some forms of bante, feldspar, dolomite, etc 
From spodumene it is distinguished by the phos- 
phorus reaction and the acid water, from the 
others by its easy fusibility 

Occurrence Amblygomte is found in granite 
and in pegmatite veins associated with other 
lithium compounds, tourmaline, cassitente and 
other minerals of pneumatolytic origin In all cases it also is probably 
a result of pneumatolytic action associated with the last phases of granite 
intrusions 

Localities The mineral occurs near Pemg, in Saxony, at Arendal, 
in Norway, at Montebras, France, at Hebron, Paris and Peru, Maine, 
at Branchville, Conn , at Pala, m California, and near Keystone, in 
the Black Hills, South Dakota 

Uses and Production The mineral is the pnncipal source of lithium 
compounds in the United States. It is used in the manufacture of 
LiCOa, which is employed as a medicine, in making mineral waters, in 
photography and in pyrotechnics 

It has been mined m South Dakota and in California to the extent 
of a couple of thousand tons, valued perhaps at $20,000. 

Dufrenite QfeaCOHJsPO*) 

Dufreiute, or kraunte, is a basic iron phosphate containing 62 per 
cent FegOs, 27 5 per cent P20s and 10 5 per cent water It may be 
regarded as a normal phosphate in which one H atom of HsP04 has been 
replaced by the Fe(OH)2 group and two by the group Fe(OH), thus 



It forms small orthorhombic crystals with a cubic habit that are rare 
Their axial ratio is .3734 i .4262. It usually occurs massive, in 



276 



DESCRIPTIVE MINERALOGY 



nodules, or in fibrous radiating aggregates The same substance is 
belie\ ed to occur also in the colloidal condition under the name ddvauute 

The color of dufremte varies from leek-green to dark green, which 
alters on exposure to yellow and brown It is translucent to opaque, 
has a light green streak and is strongly pleochroic Its hardness is 
3 5-4 and specific gravity about 3 3 

In the closed tube it yields water and whitens It fuses easily, color- 
ing the flame bluish green and yielding a magnetic globule It is sol- 
uble in HC1 and in dilute H 2 S04 

It is recognized by its color and the presence in it of water, phos- 
phorus and iron 

Localities and Origin The mineral has been observed at several 
points in Europe, at Allentown, New Jersey, and in Rockbridge County, 
Virginia It is thought to be produced by the weathering of other fer- 
ruginous phosphates 

LazuHte ((Mg Fe)(AlOH) 2 (PO 4 ) 2 ) 

Lazulite is essentially an isomorphous mixture of the two com- 
pounds Mg(A10H) 2 (P04)2 and Fe(AlOH) 2 (POi) 2 There is also fre- 
quently present m it a little calcium 
When the proportion of the two 
molecules present is as 2 . i the com- 
position becomes FeO = 77, MgO 
= 85, A1 2 3 = 32 6, P 2 5 = 4S 4 and 
H 2 0= S 8 

The mineral occurs m blue pyram- 
idal crystals that are monoclimc 
(prismatic class), with the axial ratio 
= 9750 i i 6483 and 0=89 14' 
The predominant forms are +P(nT), 
FIG 157 Lazulite Crystals A with P(lli) and P 56 (ioi)(Flg 157-4) 
-P, in (p) H-P, nl (e) and P 65 , xhe angle in A if i = 79 40' Twins 




ioi (/) B is the same combination 
twinned about oo p oo (100) with oP 
(ooi) the composition face 



are not common Those most fre- 
quently found are twinned about c 
as the twinning axis (Fig 1576) 
It is found also massive and in granular aggregates 

The cleavage of lazuhte is not distinct Its fracture is uneven It 
is brittle, has a vitreous luster, is translucent or opaque, has an azure 
color and a white streak Its hardness is 5 or 6 and its specific gravity 
about 3 i Translucent crystals are strongly pleochroic in deep blue 
and greenish blue tints the former when viewed along the vertical 



PHOSPHATES, ARSENATES AND VANADATES 277 



axis Their indices of refraction for yellow light are a= i 603, /?= i 632, 
7 =i 639 

In the closed tube lazuhte swells, whitens and yields water When 
heated in the blowpipe flame it whitens, falls to pieces and colors the 
flame bluish green The white powder moistened with Co(NOs)2 and 
reheated regains its blue color. When moistened with HgSC^ and 
heated in the blowpipe flame it imparts to it a green blue color It is 
infusible and is unacted upon by acids 

Lazulite, when massive, closely resembles in appearance massive 
forms of some varieties of sodahte, hauymte and lazunte (p 333) The 
latter, however, are soluble in HC1. Moreover, none of them contains 
phosphorus 

Occurrence The mineral occurs in quartz veins in sandstones and 
slates and is usually a product of metamorphism It is sometimes, how- 
ever, found in serpentine rocks, with corundum, in which case it may be 
original 

Localities Good crystals occur at Kneglach, in Styna, at Horrs- 
joberg, in Sweden, and in the United States at Crowder's Mountain, 
North Carolina, and on Graves Mountain m Georgia, 



OLIVENITE GROUP 

The ohvenite group includes a number of basic copper, lead and 
zinc compounds of the general formula R"o(OH)R'"04 m which R" 
= Cu, Zn, Pb and R'"=As, P, V The group is 
orthorhombic (bipyramidal class), with axial ratios 
approximating 95 . i 70 The most important 
members of the group are the two copper min- 
erals, ohvemte, Cu(CuOH) As04 and libethemte, 
Cu(CuOH)P04 

Ohvenite occurs m fibrous, globular, lamellar, 
granular and earthy masses and in prismatic and 
acicular crystals bounded by oo P(uo), oo P 60 (100), 
oo P 06 (oio), P & (on) and P 56 (101) (Fig 158) 
Their axial ratio is 9396 i . 6726 and the angle 
1 10 A 1 10= 86 26'. Their cleavage is poor. 

The mineral is some shade of green, brown, 
yellow or grayish white and its streak is olive-green 
m greenish varieties. It is transparent to opaque, is brittle, has a 
hardness=3, and a specific gravity =4.3. Its refractive indices for 



to 158 Ohvenite 
Crystal with oo Poo, 
zoo (a), oo p, no 
(m), oo Poo ,010 (6), 
P oo , on (e) and 
P 55 , 101 () 



278 DESCRIPTIVE MINERALOGY 

ydlow light are about i 83. Its luster is usually vitreous Fibrous 
vaneties are sometimes known as wood-copper 

Ohvemte fuses easily (2) to a mass that appears crystalline on cooling 
It gives the usual reactions for EkO, Cu, and As It is soluble in acids 
and in ammonia 

It is associated with other copper compounds in some copper ores 
Its ongin is secondary in all cases It occurs in the Tmtic district, 
Utah, and in many copper veins in Europe and in South America 

Libethenite occurs in compact or globular masses and in small 
crystals that resemble those of ohvemte Their axial ratio is 9605 : 
i 7019 and no A 110=87 40' 

The mineral is bnttle Its fracture is indistinctly conchoidal Its 
color is dark ohve-green and its streak a lighter shade It is translucent 
or transparent and has a resinous luster Its hardness =4 and sp gr 
=37. Its intermediate refractive index for yellow light is i 743 

When heated in the closed tube it yields water and blackens It is 
easily fusible (2) It yields the usual reaction for Cu and P, and is sol- 
uble m acids and in ammonia It is distinguished from ohvemte by the 
reaction for phosphorus 

It occurs at many of the localities for ohvemte, where, like this min- 
eral, it is a decomposition product of other copper compounds. 



Eerderite (CaBe(OH'F)P0 4 ) 

Herdente is an isomorphous mixture of the two phosphates, CaBeFP04 
and CaBe(OH)P04. The latter molecule occurs in nature as hydro- 
kerdente, the former occurs only in mixtures The theoretical compo- 
sition of the fluorine (I) and bydroxyl (II) molecules and of transparent 
crystals from Stoneham (III), and Pans (IV), Maine, are given below 

BeO CuO P 2 5 F H 2 Ins. 

. . . 100 

5 59 - ioo 

3 70 99 67 

44 ioo 51 

The mineral is found only in crystals, which are monoclmic, with 
a : b : $=.6301 : i : .4274 and =89 $4*. Their habit is hexagonal, 
pyramidal or short prismatic, elongated in the direction of a 



I- IS 39 


34 33 


43 53 


ii 64 


II. 15 53 


34 78 


44 10 




III. 15 51 


33 67 


43 74 


5 27 


rv. 16 13 


34 04 


44 OS 


53S 



PHOSPHATES, ARSENATES AND VANADATES 279 

Herdente is colorless or light yellow, transparent or translucent 
Its refractive indices are a= i 592, /3= i 612, y= i 621 

Its density is about 3, diminishing, as the amount of hydroxyl in- 
creases, to 2 952 in the pure hydroherderite 

Before the blowpipe herderite first phosphoresces with an orange- 
yellow light, then fuses to a white enamel, colors the flame red and yields 
fluorine In the closed glass tube most specimens yield an acid water, 
which, when strongly heated, evolves fluorine that etches the glass 
The mineral also reacts for phosphorus with magnesium nbbon It is 
slowly soluble in HC1 

Occurrence^ Origin and Uses Herderite occurs m pegmatite dikes 
at Stoneham, Hebron, and other places in Maine, and at the tin mines of 
Ehrenfriedersdorf, Saxony, in all of these places it is apparently of 
pneumatolytic origin The material from Maine is used to a small 
extent as a gem stone 

ACID PHOSPHATES 

Acid phosphates are those m which all of the hydrogen atoms of the 
acids have not been replaced by metals or by basic radicals Theoret- 
ically, they contain replaceable hydrogen atoms There are 12 or 15 
minerals that are thought to belong to this class, but the composition 
of many of them is very obscure Most of them appear to be hydrated 
The only important mineral that may belong to the class is the popular 
gem stone, turquoise. This, according to the best analyses, contains its 
components in the proportions indicated by the formula CuO, 3Al 2 Os, 
2P 2 Os, 9H20, which may be interpreted as (CuOH)(Al(OH) 2 ) 6 H 5 (P04)4, 
which is 4(HsP(>4), in which 6 hydrogen atoms are replaced by 6Al(OH)s 
groups and one by the group CuOH. 

Turquoise ((CuOH)(Al(OH) 2 )6H 5 (P0 4 )4) 

Turquoise is apparently a definite compound of the formula indicated 
above, which requires 34 12 per cent P 2 0s, 36 84 per cent Al 2 0a, 9 57 
per cent CuO and 19 47 per cent H20 Analysis of a crystallized variety 
from Lynch, Campbell Co , Virginia, gave 

P 2 5 A1 2 3 Fe 2 3 CuO H 2 Total 

34 13 36 5 2I 9 20 I2 99 96 

Most specimens, however, have not as simple a composition as this 
They are probably isomorphous mixtures of unidentified phosphates. 



280 DESCRIPTIVE MINERALOGY 

The mineral as usually found is apparently an amorphous or cryp- 
tocrystalline, translucent or opaque material with a wa\y lustei and a 
sky-blue, green or greenish gray color Material recently found at 
Lynch, Virginia, however, occurs in minute tnclmic crystals with an 
axial ratio 7910 . i 6051, \Mtha=87o2 / ? /3=86 2q', and 7= 72 19' 
Their habit is pyramidal with ooP 60(100), oop 06(010), oo 'P(iTo), 
ooP'(no) and POO (oil) 

The fracture of turquoise is conchoidal. It has a hardness of 5-6 
and a specific gravity between 261 and 2 89 It is brittle, and has cleav- 
ages in two directions. The determined refractive indices of the Vir- 
ginia crystals are: a=i.6i, 7= 1.65 

In the closed tube the mineral decrepitates, yields water and turns 
black or brown It is infusible, but it assumes a glassy appearance when 
heated before the blowpipe and colors the flame green. When moistened 
with HC1 and again heated the flame is tinged with the azure blue of 
copper chloride The mineral reacts for copper and phosphoric acid 
Some specimens dissolve m HC1, but the crystallized material from Vir- 
ginia is insoluble until after it is strongly ignited It partly dissolves 
in KOH, with the production of a brown residue of a copper compound 

Occurrence Turquoise occurs in thin veins cutting through certain 
decomposed volcanic rocks and other rocks in contact with them, 
and in grains disseminated through them, in stalactites, globular 
masses and crusts It is probably an alteration product of other com- 
pounds 

Localities Turquoise is found in narrow veins and irregular masses 
in the brecciated portions of acid volcanic rocks and the surrounding clay 
slates, near Nish&pur, in Persia, in the Megara Valley, Sinai, and near 
Samarkand, in Turkestan In all these places the mineral is of gem 
quality and until recently nearly all the gem turquoise came from them 
Within late years gem turquoise has been discovered in the Cenllo Moun- 
tains, near Santa Fe, New Mexico, where it has been mined in consid- 
erable quantity The locality is the site of an ancient mine which was 
worked by the Mexicans It is also found and mined in the Burro 
Mountains, Grant County, in the same State, near Millers, and at other 
points in Nevada and near Mineral Park, Mohave County, Arizona, 
where also the ancient Mexicans once had mines At La Jara, Conejos 
County, Colorado, old mines have likewise been opened up and are now 
yielding gem material 

Uses The only use of turquoise is as a gem stone Though much 
of the American mineral is pale or green, some of it is of as fine color as 
the Oriental stone A favorite method of using the stone is in its 



PHOSPHATES, ARSENATES AND VANADATES 281 

matrix Small pieces of the rock with its included turquoise are pol- 
ished and sold under the name of turquoise matrix 

Production The total value of the turquoise and turquoise matrix 
produced in the United States during 1911 was $44,751 This weighed 
about 4,363 pounds In several previous years the production reached 
about $150,000, but in 1912 it was valued at only $10,140 

HYDROUS PHOSPHATES AND ARSENATES 
HYDRATED NORMAL PHOSPHATES AND ARSENATES 

Of the hydrous salts of orthophosphonc and orthoarsemc acids there 
are two which are of some importance because they are fairly common, 
a third which is utilized in jewelry, and a fourth that is important as an 
indicator of the presence of an ore of cobalt. The first two are wwanite 
and scorodtte, a phosphate and an arsenate of iron, the third is vanszite, 
an aluminium phosphate, and the fourth is erytknte, an arsenate of 
cobalt A dimorph of vanscite, known as lucmite, is rare All give 
water in the closed tube and yield phosphine when fused with magne- 
sium and moistened with water 

VIVIANITE GROUP 

The only important group of the hydrated orthophosphates and 
orthoarsenates is that of which viviamte and erythnte are members. 
The general formula of the group is R" 3 (R'"0 4 ) 2 8H 2 in which R" 
=Fe, Co Ni, Zn and Mg, and R'"=P or As Although some members 
have not been found in measurable crystals, crystals of all have been 
made in the laboratory, so that there is little doubt of their isomorphism. 
All are monochmc prismatic with axial ratios of about 75 i : 70 and 
ft about 74 The group is as follows 

Bob^ente, Mg 3 (P0 4 ) 2 8H 2 ErytMte, Co 3 (As0 4 ) 2 8H 2 

Hornes^te, Mg 3 (As0 4 )2 8H 2 Annabcrgde, Nm(As0 4 ) 2 8H 2 

Vtwamte, Fe 3 (P0 4 )2 8H 2 Cabrente, (Ni Mg) 3 (As0 4 ) 2 8H 2 O 

Symplestte, Fe 3 (As04)2 8H 2 Kottigite, Zn 3 (As0 4 ) 2 8H 2 



Only vivianite, erythnte and annabergite are described 

Vivianite (Fe 3 (P0 4 ) 2 8H 2 O) 

Vivianite is a common phosphate of iron It occurs not only in dis- 
tinct crystals but also as bluish green stains on other minerals, and as 
an invisible constituent of certain iron ores, thereby diminishing their 
value. 



282 DESCRIPTIVE MINERALOGY 

Its formula indicates the presence of 43 per cent FeO, 28 3 per cent 
P20s and 28 7 per cent BkO 

Viviamte crystals are monoclmic (prismatic class), usually with a 
prismatic habit Their axial ratio is 7498 . i 7015, and =75 34' 
The principal forms observed on them are oo P 56 (100), oo P ob (oio), 
ooP(no), oP3(3io), P&O(IOI), P(III) and oP(ooi) The angle 
uoAi"io=7i 58' The mineral also occurs in stellate groups, in glob- 
ular, fibrous and earthy masses and as crusts coating other compounds 

Its cleavage is perfect parallel to oo P D (oio) It is flexible in 
thin splinters and sectile. The fresh, pure mineral is colorless and trans- 
parent, but specimens usually seen are more or less oxidized and have 
a blue or green color It has a vitreous to pearly luster Its streak is 
white or bluish, changing to indigo-blue or brown on exposure to the air 
Its pleochroism is strong in blue and pale yellow tints Its hardness 
is i 5-2 and density about 2 6. Its refractive indices for yellow light 
are a=i 5818, jS-i 6012, 7-1 6360 

In the closed tube viviamte whitens, exfoliates and yields water at a 
low temperature It fuses easily (2), tingemg the flame bluish green 
Its fusion temperature is 1114. The fused mass forms a grayish black 
magnetic globule. It gives the reaction for iron, and is soluble in HC1 

The mineral is easily recognized by its softness, easy fusibility and 
by yielding the test for phosphorus. 

Synthesis Crystals have been made by heating iron phosphate with 
a great excess of sodium phosphate for eight days 

Occurrence and Origin. Vivianite occurs in veins of copper, tin and 
gold ores; disseminated through peat, clay, and limomtc, coating the 
walls of clefts in feldspars and other minerals of certain igneous rocks, 
and partially filling cavities in fossils and partly fossilized bones It is 
usually the result of the decomposition of other minerals 

Localities, Crystals are found at several points m Cornwall, Eng- 
land, at the gold mines at Verespatak, in Transylvania, at Allentown, 
Monmouth County, New Jersey, and at many other places The earthy 
variety occurs at Allentown, Mullica Hill and other points in New Jer- 
sey, in Stafford County, Virginia, and in swamp deposits at many places 
It is abundant in limomte at Vaudreuil, in Quebec, and in bog iron ores 
elsewhere. 

Erythrite (Co 3 (As0 4 ) 2 8H 2 0) 

Erythnte, or cobalt bloom, isinot a common mineral, but, because 
of its beauty and the fact that it is the usual alteration product of cobalt 
ores, it deserves to be described 



PHOSPHATES, ARSENATES AND VANADATES 283 

In composition erythnte is 37 5 per cent CoO, 38 4 per cent As 2 5 , 
and 24 i per cent H20 It usually, ho\\e\er, contains some iron, nickel 
and calcium 

The mineral is isomorphous with vivianite Its crystals are mono- 
climc and prismatic or acicular and their axial ratio is 7037 i 7356 
and jS=74 5 1 ' The pnsms are stnated vertically Erythrite occurs 
in all the forms in which vivianite is found Its crystals are usually 
bounded by ooP 03(010), ooP(no), oop 66(100), +Po6(Toi) and 



The cleavage of erythnte is perfect parallel to oo P ob (oio) It is 
transparent or translucent, has a gray, crimson or peach-red color, 
and a white or pink streak Its hardness varies between i 5 and 2 5 
and its density is 295 Its luster is pearly on oo Poo (oio) and 
vitreous on other faces It is flexible and sectile. Its refractive 
indices for yellow light are a i 6263, 0= i 6614, 7= i 6986 

In the closed tube ery thrite turns blue and yields water at a low tem- 
perature At a high temperature it yields As20<j, which condenses in 
the cold portion of the tube as a dark sublimate It fises at 2, and 
tinges the flame pale blue On charcoal it fuses, yields arsenic fumes and 
a gray globule which colors the borax bead a deep blue The mineral 
is soluble in HC1, giving rise to a pink solution, which, upon evaporation 
to drynesSj gives a blue stain 

It is easily recognized by its color and the cobalt reaction. It is 
readily distinguished from pink tounna\ne (p 434), by its hardness 
and easy fusibility 

Synthesis Crystals have been obtained by carefully mixing to- 
gether warm solutions of CoSO-i and HNa2As04 7HsO 

Occurrence Erythnte occurs in the upper portions of veins con- 
taining cobalt minerals, being formed by their weathering 

Localities Tt occurs as scales and crystals at Schneeberg, Saxony, 
and as crystals at Modum, Norway. It is found, also, at Lovelock's 
Station, Nevada, at several points m California and in large quantities 
at Cobalt, Ontario. 

Annabergite (Ni3(As0 4 )2-8H 2 0) 

Annabergite, or nickel bloom, is isomorphous with erythnte It 
occurs massive, disseminated m tiny grains through certain rocks, as 
crusts and stains m globular and earthy masses, and in fibrous crystals, 
the axial ratios of which are not known. 

The mineral is apple-green in color, and is translucent or opaque. 



284 DESCRIPTIVE MINERALOGY 

Its streak is light green Its luster is vitreous, its hardness, i 5-2 5 
and sp gr =3 

Before the blowpipe it melts to a gray globule and gives the arsenic 
odor In the closed glass tube it blackens and yields water In the 
beads it gives the usual reactions for Ni The mineral dissolves easily 
in acids 

Synthesis Crystals have been produced by the method employed 
in the synthesis of erythnte, using NiSO-i, instead of CoSC>4 

Occurrence It is found as a common alteration product of nickel- 
bearing minerals, in the oxidized portions of veins 

Localities Its best known occurrences are m Allemont, Dauphme, 
Annaberg and Schneeberg, Saxony, Cobalt, Ontario, and mines in 
Colorado and Nevada. 



Variscite (A1P0 4 2H 2 0) 

Vanscite is a bright green mineral that has recently come into use as 
a gem material. It is apparently an aluminium phosphate with a 
theoretical composition as follows 449 per cent P20r>, 32 3 per cent 
AloOa and 228 per cent H^O A specimen of crystallized material from 
Lucm, Utah, gave the following analysis 

P 2 5 A1 2 3 Fe 2 3 Cr0 3 V 2 3 H 2 Total 

44 73 32 40 06 18 32 22 68 100 37 

Recent investigations indicate that the compound A1P04 2H 2 is 
dimorphous Both forms are orthorhombic but one, vanscite, has the 
properties described under this heading The other, lucinite, is associ- 
ated with vanscite, near Lucm, Utah. It, however, occurs in crystals 
that are octahedral in habit, rather than tabular, and that have an 
axial ratio of 8729 i 9788 In other respects lucimte is very much 
like variscite 

An amorphous variety of the same substance is also known It 
occurs as a white, pale brown or pale blue earthy mass with a sp gr of 
2.135 It differs from the crystalline varieties in being completely 
soluble in warm concentrated H 2 S04 

The crystals of vanscite are orthorhombic and are bounded by 
co P 66 (oio), oo P(no) and P oo (012), and in a few cases oo P 60 (too) 
Their axial ratio is 8944 .1:1 0919 Nearly all crystals are tabular 
parallel to oo P 56 (oio) Twins are common, with |P 60 (102) the 
twinning plane Crystals are comparatively rare, the mineral occur- 
ring usually in fibrous or finely granular masses and as incrustations 



PHOSPHATES, ARSENATES AND VANADATES 285 

Vanscite vanes in color from a pale to a bright green It is weakly 
pleochroic, has a vitreous luster, a hardness of about 4 and a density of 
2 54 Its refractive indices for yellow light are a=i 546, /3=i 556, 
r =i 578 

Before the blowpipe the mineral is infusible It, however, whitens 
and colors the flame deep bluish green It )ields water in the closed 
tube, and with the loss of its water, it changes color from green to 
lavender The same change in color takes place gradually at temper- 
atures between iio-i6o When heated with Co(N03)2, it turns blue 
and when fused with magnesium ribbon it gives the test for phosphorus 
It forms a yellowish green glass with borax or microcosmic salt. The 
mineral is insoluble in acids before heating 

Vanscite resembles m some respects certain varieties of turquoise 
and wwuellite (p 287) It is distinguished from turquoise by the absence 
of copper and from wavellite by its insolubility in acids 

Occurrence The mineral occurs as a cement in a brecciated, cherty 
limestone and a brecciated rhyolite, as nodules m the cherty portions 
of the breccias and also as veins traversing these rocks It is also 
found as nests in weathered pegmatites The crystals occur as coarsely 
granular, loosely coherent masses in more compact granular masses 

Localities Vanscite occurs at Messbadi, Sa\ony, in Montgomery 
County, Arkansas, near Lucm, Utah, and at a number of other places 
in Tooele and Washington Counties in this State, in Esmeralda County, 
Nevada, and m Montgomery County, Arkansas The colloidal vanety 
occurs as concretions in slates at Brandberg, near Leoben, Austria 

Uses The mixture of vanscite and rock is cut, and employed as 
sets in necklaces, belt pins, etc , under the names " utahlite " and 
" amatrice," but because of the softness of the vanscite it cannot be 
used with success for all the purposes for which turquoise matrix is 
used 

Production The production of the material in the United States 
during 1911 was 540 Ib , valued at $5,750 In the previous year 
5,377 Ib were reported as having been sold for $26,125, I n I 9 I2 > 
the amount marketed was valued at $8,150. 



Skorodite 

Skorodite is more common than viviamte It occurs in globular 
and earthy masses, as incrustations, and in crystals of a green or brown 
color The globular forms are colloidal 

Its formula indicates Fe203=346 per cent, Asa03=49 8 P er cent 





286 DESCRIPTIVE MINERALOGY 

and HoO= 15 6 per cent An incrustation on the deposits of the Joseph's 
Coat Spring, Yellowstone National Park, consisted of 

As 2 O 5 Fe 2 O 3 H 2 O SiO 2 SO 3 Total 

46 48 33 2 9 I 5 5 4 35 8 4 100 46 

Its crystallization is orthorhombic (bipyramidal class), with a b . c 
8658 . i 9541. The crystals, which are commonly bounded by 
oo P 60(100), oo P 06(010), ooPa(i2o), ooP(uo), 
P(III) and -2-P(ii2), are either prismatic or octa- 
hedral m habit (Fig 159) The angle niAiTi 
= 65 20' Their cleavage is imperfect, parallel to 
ooP(no) 

The mineral is brittle It has a vitreous luster, 
a leek-green or liver-brown color and a white 
streak. It is translucent and has an uneven frac- 
ture Its hardness is 3 5-4 and density about 3 3 
FIG 159 Skorodite The colloidal phases are somewhat softer than the 
Crysta wit oo co , cr y sta }} me phases 
100 (a) oo P 2, 1 20 

(d) and P m (p) In "the closed tube skorodite turns yellow and 

' yields water It fuses easily, coloring the flame 

bluish. On charcoal it yields white arsenical fumes and gives a black 

porous, magnetic button It is soluble in HC1, forming a brown solution 

It is distinguished from wviamte by the arsenic test, and from dufren- 

%te by its streak and reaction in the closed tube 

Synthesis Skorodite crystals have been made by heating metallic 
iron with concentrated arsenic acid solution at I4o ~i$o 

Occurrence. Skorodite is frequently associated with arsenopynte, 
in the oxidized portions of veins containing iron minerals It is found 
also in a few places as incrustations deposited by hot springs, 

Localities It occurs m fine crystals at Nerchinsk, Siberia; at 
Loelling, m Cannthia, near Edenville, New York, in the Tmtic dis- 
trict, Utah, and as an incrustation on the siliceous sinter of the geysers 
in Yellowstone Park. 

HYDRATED BASIC PHOSPHATES AND ARSENATES 

The hydrated basic phosphates and arsenates are rather more nu- 
merous than the hydrated normal compounds, but most of them are rare 
One, waveltite, however, is a handsome mineral that is fairly common. 
Another, pharmacosiderite, an iron arsenate, is known to occur at a 
number of places The uramte group also belongs here Its members 



PHOSPHATES, ARSENATES AND VANADATES 287 

are comparatively rare, but, because of the presence of uranium in them, 
they are of considerable interest 

Wavellite ((A1(OH F) 3 )(PO 4 ) 2 5 H 2 O) 

Wavellite rarely occurs in crystals It is usually in acicular aggre- 
gates that are either globular or radiating (Fig 160) The few crystals 
that have been seen are orthorhombic (bipyramidal class), with an 
axial ratio of 5573 i . 4057 

Its composition varies widely, and frequently a fairly large portion 
of the OH is replaced by F, and a portion of the Al by Fe 

The mineral is vitreous in luster and white, green, yellow, brown or 
black in color Its streak is white It is brittle and translucent, m- 




FIG 1 60 Radiate Wavellite on a Rock Surface 

fusible and insoluble m acids Its hardness is 3 5 and its density 2.41. 
Its intermediate refractive index for yellow light is i 526. 

Heated m a dosed glass tube, wavelhte yields water, the last traces 
of which react acid and often etch the glass In the blowpipe flame the 
mineral swells up and breaks into tiny infusible fragments, at the same 
time tingeing the flame green. The mineral is soluble in HC1 and 
H2SO4. When heated with HaS04 many specimens yield hydrofluoric 
acid When heated on charcoal and moistened with Co(NOs)2 and 
reheated, the mineral turns blue. 

Wavellite is distinguished from turquoise, which it sometimes 
resembles, by its action in the blowpipe flame, by its inferior hardness 
and its manner of occurrence 

Occurrence Wavellite occurs as radiating bundles on the walls of 



288 DESCRIPTIVE MINERALOGY 

cracks in various rocks and as globular masses filling ore veins and the 
spaces between the fragments of breccias It is probably m all cases 
the result of weathering 

Localities It is found at a great number of places, especially at 
Zbirow, in Bohemia, at Mmas Geraes, Brazil, at Magnet Cove, Arkan- 
sas, and in the slate quarries in York County, Penn. 

Pharmacosidente ((FeOH) 3 (AsO 4 )2 5H 2 O) 

Pharmacosiderite is a hydrated ferric arsenate, the composition of 
which is not firmly established It usually occurs m small isometric 
crystals (hextetrahedral class), that are commonly combinations of 

ooQoo(ioo) and (in) It is also sometimes found in granular 
i 

masses Its cleavage is parallel to oo o (100) 

The mineral is green, dark brown or yellow. Its streak is a pale 
shade of the same color It has an adamantine luster and is translucent. 
Its hardness = 25 and sp gr =3 It is sectile and pyroelectnc Its 
refractive mde\, =i 676 

Pharmacosiderite reacts like skorodite before the blowpipe and with 
reagents 

The mineral occurs m the oxidized portions of 01 c \ ems, in Cornwall, 
England, at Schneeberg, Saxony, near SchemmU, Hungai} , and in the 
Tintic district, Utah. 

URANITE GROUP 

The uramtes are a group of phosphates, arsenates and vanadates 
containing uranium m the form of the radical uranyl (UOs) which is 
bivalent The members of the group are either tetragonal, or ortho- 
rhombic with a tetragonal habit They all contain eight molecules of 
water of crystallization Only three members of the group are of 
sufficient interest to be discussed here These are the hydrated cop- 
per and calcium uranyl phosphates, torbermte and aittumte and the 
potassium uranyl vanadate, carnotite 

The entire group so far as its members have been identified is as 
follows. 

Awlumte Ca(U0 2 )2(P0 4 )2 8H 2 Orthorhombic 

Uranospwite Ca(U0 2 }2(As04) 2 SBfcO Orthorhombic 

Torb&rmte Cu(U0 2 )2(P04) 2 8H 2 Tetragonal 

Zeunente Cu(U0 2 ) 2 (As04) 2 8H 2 Tetragonal 

Uranocirate Ba(U02)2(P04) 2 8H 2 Orthorhombic 

Camohte (Ca 



PHOSPHATES, ARSENATES AND VANADATES 289 

The uramtes are of interest because of their content of uranium, an 
element which is genetically related to radium 



Autunite (CaCUCbMPO^ 8H 2 O) 

Autunite occurs in thin tabular crystals with a distinctly tetragonal 
habit, and in foliated and micaceous masses 

The percentage composition corresponding to the above formula 
is 6 i per cent CaO, 62.7 per cent UOs, 15 5 per cent PsOs and 15 7 per 
cent H 2 O 

Its crystals are orthorhombic (bipjrraimdal class), with an axial 
ratio, p875 : i 28517, thus possessing interfacial angles that closely 
approach those of torbermte. Its crystals are bounded by oP(ooi), 
P a (101), P 06 (on), and several less prominent planes Their cleav- 
age is very perfect and the cleavage lamellae are brittle The luster is 
pearly on the base and vitreous on other surfaces. 

The mineral is lemon-yellow or sulphur-yellow in color, and its streak 
is yellow It is transparent to translucent. Its hardness is 2-2 5 and 
its specific gravity about 3 2. Its refractive indices for yellow light are. 

= i 553,0=1 S7S>7=i577 

The mineral reacts like torbermte before the blowpipe and with acids, 
except that it shows none of the tests for copper. It is recognized by its 
color, streak and specific gravity 

Occurrence Autunite occurs m pegmatite veins and on the walls 
of cracks in rocks near igneous intrusions, especially in association with 
other uranium compounds, of which it is a decomposition product. 

Localities. It has been found at Johanngeorgenstadt, Germany, 
at Middletown and Branchville, Conn , in the mica mines of Mitchell 
County, North Carolina, and coating cracks in gneiss at Baltimore, Md 



Torbernite (CuCUOs^CPO^ -8H 2 0) 

Torbermte occurs in small square tables, that may be very thin or 
moderately thick, and in foliated and micaceous masses. 

The pure mineral contains 612 per cent UOs, 8 4 per cent Cu, 
15 i per cent P20s and 15.3 per cent H2<D, but frequently a part of the P 
is replaced by As 

Its crystals are tetragonal (ditetragonal bipyramidal class), with 
a c= i . 2 9361 They are extremely simple, their predominating 
forms being oP(ooi) and POD (101). Less prominent are ooPoo (100), 
sPoo(2oi) and ooP(no) Their cleavage is perfect parallel to oP 
The cleavage lamellae may be almost as thin as those of the micas 
but they are brittle 



290 DESCRIPTIVE MINERALOGY 

The mineral is bright green in emerald, grass or apple shades, has a 
lighter green streak, is translucent or transparent, and has a hardness 
of 2 25 and a specific gravity of about 3 5 Its luster is pearly on the 
basal plane but nearly vitreous on other burfaces It is strongly pleo- 
chroic in green and blue. 

Torbermte gives reactions for Cu and P and yields water in the 
closed tube The bead reactions for uranium are masked by those of 
copper The mineral is soluble in HN0 3 

The mineral is easily recognized by its color and other physical 
properties 

Occurrence. Torbermte is occasionally found as a coating on the 
walls of crevices in rocks It occurs in Cornwall, England, at Schee- 
berg, Saxony, at Joachimsthal, Bohemia, and at most places where other 
uranium minerals exist It is probably in all cases a weathering product. 

Carnotite ((Ca KsXTTC^MVO^ xHaO) 

Carnotite, like the other uramtes described, is extremely complex 
in composition It may be an impure potassium uranyl vanadate, or a 
mixture of several vanadates in which the potassium uranyl compound 
is the most prominent The formula given above indicates its com- 
position as well as any simple formula that has been proposed A 
specimen from La Sal Creek, Colorado, shows the mineral to be essen- 
tially as follows ' 



UOs CaO BaO K 2 H 2 at 105 H 2 above 105 
18 05 54 oo i 86 i 86 5 4^ 3 16 2 21 

though there are present in the specimen analyzed, or in other specimens 
from the same locality, also As 2 3 , P 2 O 5 , Si0 2 , Ti0 2 , C0 2 , S0 3 , Mo0 3 , 
Cr 2 3 , Fe 2 3 , A1 2 3 , PbO, CuO, SrO, MgO, Li 2 and Na 2 0, and there 
are reported in them also small quantities of radium Radiographs 
taken with the aid of carnotite have been published, which are almost 
as clear as those taken with pitchblende The complete analysis of a 
specimen from the Copper Prince Claim, Montrose Co , Colo , gave: 



V 2 5 
1835 

CuO 

20 

Also 
Na 2 0= 


As 2 5 
25 

CaO 

285 

TiOa=. 
.09 


P 2 5 
33 

BaO 

.72 

10, C0 2 = 


U0 3 MoOg Fe 2 3 
5 2 25 23 i 77 

K 2 H 2 0- H 2 0+ 
6 73 2 59 3 06 

33, S0 3 =.i2, CrOs=tr, 


A1 2 3 
i. 08 

Ins 
8 34 

MgO= 


PbO 

25 
Total 
99 84 
20 and 



PHOSPHATES, ARSENATES AND VANADATES 291 

The mineral has been found only in tiny crystalline grams, so that its 
physical properties are not well known It is bright yellow in color, and 
is completely soluble in HNOs If to the nitric acid solution hydro- 
gen peroxide be added a brown color will appear Or if the solution 
is filtered, made alkaline by ammonia and through it is passed H2S, a 
garnet color will develop If the mineral be moistened by a drop of 
concentrated HC1, a rich brown color will result The addition of a drop 
or two of water will change the color to light green or make it disappear 

Occurrence Carnotite occurs as a yellow crystalline powder, some 
of which seems to consist of minute crystals with an hexagonal habit, 
in the interstices between the grains in sandstones and conglomer- 
ates, as nodules or lumps in these rocks, and as coatings on the walls 
of cracks in pebbles in the conglomerates and on pieces of silicified 
wood embedded in the sandstones. It is limited to very shallow 
depths and is apparently a deposit from ground water. 

Localities Its principal known occurrences are in Montrose, San 
Miguel, Mesa and Dolores Counties in southwestern Colorado, especially 
in Paradox Valley, and in adjoining portions of New Mexico and Utah, 
and in Rio Blanco and Routt Counties in the northwestern portion of 
Colorado. At all these places there are large quantities of the impreg- 
nated rock but it contains on the average only about i 5 per cent to 
2 per cent of UsOg. The mineral has also been described from Mt 
Pisgah, Mauch Chunk, Pennsylvania, and from Radium Hill, South 
Australia 

Uses. The mineral is one of the main sources of radium and uranium 
and is one of the principal sources of vanadium. Although it contains a 
notable quantity of uranium, carnotite has little value except as an ore 
of radium and vanadium, because of the few uses to which uranium is 
put. This metal is used to some extent in making steel alloys and in the 
manufacture of iridescent glazes and glass Its compounds are used in 
certain chemical determinations, as medicines, in photography, as por- 
celain paint, and as a dye in calico printing. The uses of vanadium have 
been referred to on p 273 

The principal value of carnotite depends upon its content of radium, 
which in the form of the chloride is valued at about $40,000 per gram 
or $1,500,000 per oz The importance of radium as a therapeutic agent 
has not been established, but that its use is wonderfully helpful in many 
diseases is beyond question Without doubt in the near future carno- 
tite will become the principal source of radium in the world Practically 
the only other source is the pitchblende (p 297), of Gilpin, Colorado, 
Cornwall, England and Joachimsthal, Austria. 



292 DESCRIPTIVE MINERALOGY 

Production Carnotite has been mined in San Miguel and Montrose 
Counties, Colorado, and at several points in eastern Utah, but mainly 
for the vanadium it contains At present it is being utilized as a source 
of radium From Colorado 8,400 tons of vanadium ore, with a value 
of $302,000, were shipped in 1911 and from New Mexico and Utah about 
70 tons, valued at $3,500 Some of this, however, was vanadmite 
Most of it was exported and used as a source of vanadium However, 
the uranium content of the carnotite mined was about i r tons of the 
metal During 1912 ore containing 26 tons of uranium o\ide and 6 7 
grams of radium was produced This would have yielded n 43 grams 
of radium bromide, valued at $52,800 The present price of standard 
carnotite carrying at least 2 per cent UgOg and 5 per cent V^Os, is at the 
rate of $i 25 per Ib for the former and thirty cents for the latter In 
1914 the selling price of 4,294 tons of carnotite ore containing 87 tons 
of UsOg was $103 per ton At the present time nothing is paid for the 
radium content of the ore, though this is its most valuable component 
One ton of ore containing i per cent of UaOg carries 2 566 milligrams of 
radium The imports of uranium compounds during 191*2 were valued 
at $14,357- 

HYDRATED ACID PHOSPHATES AND ARSENATES 

A number of hydrated acid phosphates and arsenates are known to 
constitute an isomorphous group, but only a few of them occur as 
minerals. Brushite is an acid calcium phosphate and pfwrmacofate is 
the corresponding arsenate Both crystallize in the monoclimc system 
(prismatic class) Neither is common 

Pharmacohte (HCaAs0 4 2H20) occurs principally in silky fibers, in * 
botryoidal and stalactic masses and rarely in crystals with an axial 
ratio .6236 ' i : 3548 and 18=83 13'. Their cleavage is perfect par- 
allel to oo P ob (oio) The mineral is white or gray, tinged with red 
Its streak is white It is translucent or opaque Its luster is vitreous, 
except on oo P & (oio) where it is slightly pearly Thin laminae are 
flexible Its hardness is 2-2 5 and density 2 7 Its refractive indices 
for yellow light are. 01=1.5825, ]8=i 5891, 7=1 5937 

Before the blowpipe pharmacohte swells up and melts to a white 
enamel. The mineral gives the usual reactions for As, EfeO and Ca It 
usually occurs in the weathered zone of arsenical ores of Fe, Ag and Co, 
at Andreasberg, Harz; Joachimsthal, Bohemia, and elsewhere. 



CHAPTER XV 
THE COLUMBATES, TANTALATES \ND URANATES 

THE rare metah, columbium and tantalum, exist in a few silicates, 
but their principal occurrences are as columbates and tantalates which 
are salts of columbium and tantalum acids, analogous to the various 
acids of sulphur The commonest compounds are salts of the meta- 
acids EfeQteOo and H2Ta20e, the relations of which, to the normal acids, 
are indicated by the equation 2HsCb04 2H20=H2Cb206 Other im- 
portant minerals are derivatives of the pyroacids corresponding to 
HiCtaOr, or 2HsCb04 EkO The best known ortho salt is ferguson- 
tte, YCb0 4 , but it is rare 

All the columbates yield a blue solution when partially decomposed 
in EfeSQi and boiled with HC1 and metallic tin The tantalates when 
fused with KHSO* and treated with dilute HC1 give a yellow solution 
and a heavy white precipitate, which, on treatment with metallic zinc 
or tin, assumes a deep blue color When diluted with water the blue 
color of the tantalate solution disappears, whole that of the columbate 
solution remains 

The uranates are salts of uramc acid, HsUtX. The only mineral 
known that may be a uranate is urarnn/Ue 9 and the composition of this 
is doubtful. 

Columbite (CFe-Mn)Nb 2 O 6 ) and Tantalite ((Fe-Mn)Ta2O 6 ) 

These two minerals are isomorphous mixtures of iron and manganese 
columbates and tantalates The name columbite is applied to the mix- 
ture that is composed mainly of the columbates, and tantalite to that 
which is principally a mixture of tantalates When the tantalite is 
composed almost exclusively of the manganese molecule, it is known as 
manganotantal^te Tin and tungsten are frequently found in both min- 
erals 

Their crystals are orthorhombic, with a : b . c 8285 : i : 8898 for 
the nearly pure columbium compound, and 8304 : i : .8732 for the 
nearly pure tantalum compound Both form short prismatic crystals 
containing many faces, among the most prominent being the three 
pinacoids, various prisms, notably o P(no), oo Pjfoo) and oo P6(i6o), 



294 



DESCRIPTIVE MINERALOGY 





and the domes 2? 56 (201) and |P 06 (012) (Fig 161) The most promi- 
nent pyramids are P(in) and P3(i33). Twins are not uncommon, 
with 2P66 (201) the twinning plane The angle noAiIo for colum- 
bite=79 17' 

Both minerals are usually opaque, black and lustrous, and occasion- 
ally iridescent, though, in some instances, they are translucent and 
broun Their streak is dark red or black Their cleavage is distinct 
parallel to oo P 60 (100), fracture uneven or conchoidal, their hardness 

6 and their specific gravity 
between 5 3 and 73, in- 
creasing with the propor- 
tion of the tantalum mole- 
cules present They are 
both infusible before the 
blowpipe Some specimens 
exhibit weak radioactivity 
When columbite is de- 
composed by fusion with 
KOH and dissolved in HC1 

and BkSO-i, the solution 
turns blue Qn thfi addltlon 

USbdllC 1C The mm- 

eral 1S also partially decom- 
posed when evaporated to 
dryness with EfeSCU, forming a white compound that changes to yellow 
When this residue is boiled with HC1 and metallic zinc a blue solution 
results The mineral also gives reactions for iron and manganese. 

Tantalite is decomposed upon fusion with KHSQ* in a platinum 
spoon, or on foil. This when heated with dilute HCl yields a yellow 
solution and a heavy white powder Upon addition of metallic zinc, a 
blue color results and this disappears on dilution with water In the 
microcosmic salt bead tantalite dissolves slowly, giving reactions for iron 
and manganese When treated with tin on charcoal the bead turns 
green 

The two minerals may easily be confused with black fourmahne 
(p. 434), tlmemte (p 462) and wolframite From tourmaline, they are 
distinguished by crystallization, high specific gravity and luster, from 
wolframite by their less perfect deavage and by the reaction with 
aqua regia (see p 259), from ilmenite by the test for titanium 

Occurrence, Ongm and Localities. Both minerals occur in veins of 
coarse granite and probably have a pneumatolytic origin 



FIG i6i.-Columbite Crystals with 

(a). ooPoo,oio (6), oop, no (f), oP2, 210 
Ml - 730 (d), oop^o (,), |P 55, I03 

(, P, in W and PI 133 M 



COLUMBATES, TANTALATES AND URANATES 295 

Columbite is found in granite \erns at Bodenmais, Bavaria, Tam- 
mela, in Finland, near Limoges, France, with tantahte, near Miask, 
in the Ilmen Mountains, Russia, with samarskite, and at Ivigtut, m 
Greenland In the United States it is found at Standish and Stone- 
ham, m Maine, at Acworth, in New Hampshire, at Haddam, in Con- 
necticut, at Amelia Court House, Virginia, with samarskite in the mica 
mines in Mitchell County, North Carolina, m the Black Hills, South 
Dakota, and at a number of other points in New England and the Far 
West 

Tantahte is found at many of the localities for columbite and also 
at several other places in Finland, near Falun, in Sweden, in Yancy 
County, North Carolina, and m Coosa County, Alabama 

Uses At the present time columbium and its compounds have no 
commercial uses Tantalum, however, is employed in the manufacture 
of filaments for certain types of incandescent lamps Since, howe\er, 
about 20,000 filaments may be made from a single pound of the metal the 
market for tantalum ores is very limited 

Samarskite and Yttrotantalite 

These two minerals may be regarded as isomorphous mixtures of 
salts of pyrocolumbic and pyrotantalic acids, in which the bases are 
yttrium, iron, calcium and uranyl. 

Samarskite, according to this view, is approximately 

Y 2 (Ca Fe U0 2 )3(Nb 2 7 )3 

and yttrotantalite the corresponding tantalate Yttrium and iron are 
the principal bases, but there are also often present erbium, cerium, 
tungsten and tin 

Analyses made by Rammelsberg and quoted by Dana give some idea 
of the complexity of the compounds: 



Density 


Ta 2 6 Nb 2 5 W0 3 


Sn0 2 Ti0 2 * Y 2 3 


Er 2 0a 


I 5 425 


46 25 


12 32 2 36 


I 12 


10.52 


6 71 


II- 5 839 


14 36 


41 07 


16 


56 6 10 


10 80 


III 5 672 





55 34 


22 


i 08 8 80 


382 


Ce 2 3 t 


U0 2 


FeO 


CaO 


H 2 O 


Total 


I 2 22 


i 61 


380 


5 73 


6 31 


98 95 


II. 2 37 


10 90 


14 61 




. 


too 93 


HI 4 33 


ii 94 


14 3 







99 83 


I Fromltterb; 


y, Sweden 


II From North Carolina 


HI From Miask 


Russia. 



* Including SiO*, f Including Di 2 0s and La^Os 



296 DESCRIPTIVE MINERALOGY 

The first of these three minerals has been called yttrotantahte and 
the other two samarslute If the first is weathered, as seems probable 
from the presence of over SL\ per cent of water, the three may constitute 
members of an isomorphous series with the third representing the nearly 
pure columbate (sanurskite), the first a compound in which the tantalate 
molecule is in excess (yttrotantahte), and the second an intermediate 
compound which contains both the tantalum and columbmm molecules, 
with the latter predominating 

With more accurate analyses the great complexity of these compounds 
becomes even more apparent Hillebrand has given the following report 
of his analysis of a samarskite from Devil's Head Mountain, near Pike's 
Peak, Colorado, which shows the futility of attempting to represent its 
composition by a chemical formula- 

Pitch-black Black Weathered 

Variety Variety Variety 

Ta 2 fi 27 03 28 ii 19 34 

CbaOs 27 77 26 16 27 56 

W0 3 2 25 2 08 5 51 

SnO 2 95 i 09 82 

Zr0 2 2 29 2 60 3 10* 

U0 2 4 02 4 22 

U0 3 6 20 

Th0 2 3 64 3 60 3 19 

Ce 2 3 54 49 4 i 

(La,Di) 2 3 I 80 2 12 i 44 

Er 2 0s 10 71 10 70 9 82 

Y 2 3 6 41 5 96 5 64 

Fe 2 3 8 77 8 72 8 90 

FeO 32 35 39 f 

MnO 78 75 \ 

ZnO 05 07 / 77 

PbO 72 80 i 07 

CaO 27 33 i 6 1 
MgO 

K 2 17 I3 > 

(Na,Li) 2 24 17 I ^ 

H 2 0.. i 58 i 30 3 94 

F . ? ? ? 




99 75 

6 12 



f O 



COLUMBATES, TANTALATES AND URANATES 297 




Poo,ioi(e), 
3P3> 231 W 



120 



Both samarskite and yttrotantahte are orthorhombic, with an axial 
ratio for samarskite of 5456 : i : 5178, and for yttrotantahte, 5411 
i . i 1330. They, however, more commonly occur massive and in 
flattened grams embedded in rocks Their crystals are prismatic in 
the direction of the c or the b a\is Their most prominent forms are 
oo P 56 (100), oo P 66 (oio) and P 65 (101) (Fig 162) Less prominent 
but fairly common are *>P2(i2o), ooP(no), P(in) and 
The angle noAiTo for samarskite is 57 14' 
and for yttrotantahte 56 50' 

The cleavage of both minerals is indistinct 
parallel to oo P 06 (oio) Their fracture is 
conchoidal Both are brittle The hardness of 
samarskite is 5-6, its density about 5 7, its 
luster vitreous, its color velvety black and its 
streak reddish brown Yttrotantahte is a little 
softer (5-5 5) Its specific gravity is 5 5~5 9, 
its luster submetallic to vitreous, its color black, FIG 162 SamarshteCiys- 
brown, or yellow, and its streak gray to color- fed w^ oop 55 , 100 (a), 
less Samarskite is opaque and yttrotantahte p55 ' OI JW> p 
opaque or translucent 

The reactions of the minerals vary with 
their composition They always yield the 
blue solution test for tantalum or columbium, and most specimens react 
for Mn, Fe, Ti and U The reaction for uranium is an emerald green 
bead with microcosmic salt in both reducing and oxidizing flame. 

They are distinguished from columbite and t&ntahte by the form of 
their crystals. 

Occurrence The two minerals, like columbite and tantahte, are 
found principally in pegmatite veins and in many of the same localities 
Yttrotantahte occurs mainly at Ytterby and near Falun, in Sweden, and 
samarskite, near Miask in the Ilmen Mountains, Russia, In the United 
States the last-named mineral is sometimes found in large masses in the 
mica pegmatites of Mitchell County, North Carolina. 

Uses Neither mineral is at present of any commercial value. They 
are, however, extremely interesting as the source of many of the rare 
elements, and, especially, as a possible source of radium and closely 
related substances. 

Urardnite 

Uramnite, or pitchblende, like the other compounds containing the 
element uranium, is of doubtful composition. It contains so many 



298 DESCRIPTIVE MINERALOGY 

different components that a correct conception of its character is almost 
impossible to grasp The mineral is particularly interesting because it 
always contains a trace of radium, of which it is an important com- 
mercial source at the present time 

Analyses of crystallized material (I) from Branchville, Conn, 
and from Annerod (II), Norway gave the following results 

U0 3 U0 2 ThO 2 PbO Fe 2 O 3 CaO H 2 O Pie Insol 

I. 21 54 64 72 6 93 4 34 28 22 67 Und. 14 

II 30 63 46 13 6 oo 9 04 25 37 74 17 4 4 2 



\\ith small quantities also of ZrC>2, Ce02, La 2 03, D^Os, YgOs, Er 2 C>3, 
MnO, Alkalies, SiOs and P20s These analyses are interpieted as indi- 
cating that the mineral is a uranium salt of uramc acid, U02(OH)2, or 



H 2 U04, thus U^dr , or U 3 S , in which Pb replaces the U in 



part, and Th02 the UC>2 Radium is found in most specimens and 
helium in nearly all 

Several varieties aie recognized, the distinctions being based largely 
upon chemical differences 

Broggente has UOa to other bases as i : i 

Cleweite and nnvemte contain 9 per cent to 10 per cent of the yttna 
earths 

Pitchblende is possibly an amorphous urammte containing a very 
little thona and much water Its specific gravity is often as low as 6 5, 
due probably to partial alteration 

Urammte crystallizes in the isometric system in octahedrons, and m 
combinations of 0(ui), oo 0(no), and oo oo (100) Crystals are rare, 
however, the material usually occurring in crystalline masses and in 
botyroidal groups 

The mineral is gray, brown or black and opaque. Its streak is 
brownish black, gray or olive green. Its luster is pitch-like or dull Its 
fracture is uneven or conchoidal It is brittle, its hardness is 5 5 and 
density 9-9 7 Like the other uranium minerals it is radioactive 

Before the blowpipe uraninite is infusible. Some specimens color 
the flame green with copper With borax it gives a yellow bead in the 
oxidizing flame, turning green in the reducing flame All specimens give 
reactions for lead and many for sulphur and arsenic The mineral is 
soluble in nitric and sulphuric acids, with slight evolutions of helium, 



OOLUMBATES, TANTALATES AND URANATES 299 

the ease of solubility increasing with the increase in the proportion of 
rare earths present 

Urammte is distinguished from wo'Jramite, samarsktfe, columbde and 
tantahte, by lack of cleavage, greater specific gravity, and differences in 
crystallization From all but samarskite it is also distinguished by the 
reactions for uranium and, m the case of most specimens, by the reac- 
tion for lead It is especially characterized by its pitch-black luster 

Occurrence and Localities Urammte occurs in pegmatites and in 
veins associated ^ith silver, lead, copper and other ores It is found m 
the ore veins in Saxony, Bohemia, and in pegmatites near Moss, Arendal 
and other points in Norway 

In the United States it occurs in pegmatites at Middletown and 
B ranch ville, in Connecticut, at the Mitchell County mica mines, 
North Carolina, and at Barnnger Hill, Llano County, Texas It is 
also found m large quantity near Central City, Gilpin County, Colorado, 
where it is associated with gold, galena, tetrahednte, chaicopynte and 
other ore mineials 

Production Urammte has been mined in small quantity in Colo- 
rado, and at Barnnger Hill, both as a source of uranium and as a 
source of radium In Cornwall, England, and at Joachimsthal, 
Austria, it is mined as a source of radium (See also p 292.) 



CHAPTER XVI 

THE SILICATES 

THE silicates are salts of various silicon acids, only a few of which 
are known uncombmed with bases The silicates include the commonest 
minerals and those that occur in largest quantity They make up the 
greater portion of the earth's crust, forming most of the igneous rocks 
and a large portion of vein fillings In number, the silicates exceed all 
other mineral compounds, but because of their stability they are of very 
little economic importance A few are used as the sources of valuable 
substances, and their aggregates, the sihcious rocks, are utilized as 
building stones, but, on the whole, they are of little commercial value 
Since, however, they occur in good crystals and their material is trans- 
parent in thin sections so that it can easily be studied by optical methods, 
they are of great scientific importance Much of the progress made in 
crystallography has been accomplished through the study of these com- 
pounds 

Although the salts of the silicic acids are very numerous and most of 
them are very stable toward the ordinary reagents of the laboratory, 
the acids from \\hich they are derived are only imperfectly known 
The only one that has been prepared m the pure state is the compound 
KfeSiOa This occurs as a gelatinous (colloidal) white substance which 
rapidly loses water upon drying and probably breaks up into a number 
of other compounds which are also acids, containing, however, a larger 
proportion of silicon in the molecule than that in the original compound 
When the tetrafluoride, or the tetrachionde, of silicon is decomposed by 
water, the principal product is the acid referred to above, but m addition 
to this there is probably formed also the compound HaSiO* or Si(OH)4, 
which is the ortho acid Some silicates are salts of these acids. Others 
are salts of the acids containing a larger proportion of silicon In most 
cases, however, these acids may be regarded as belonging to a series in 
which the members are related to one another m the same manner as 
are normal sulphuric, common sulphuric and pyrosulphuric acids. Nor- 
mal sxilphuric acid is HeSOe By abstraction of aKkO the compound 
H 2 SO4, or ordinary sulphuric acid, results If from two molecules of 
EfcSOi, one molecule of HsO is abstracted, 1128307, or pyrosulphuric 
acid, is left. In the same manner all of the silicic acids may be regarded 

300 



SILICATES 301 

as being derived from normal silicic acid Si(OH)4 or H4SiO4 by the ab- 
straction of water, thus: 



Orthosilicic acid is 
Metasihcic acid is H4Si04 -I^Oor H 2 SiOs, 
Diorthosilicic acid is 2H4Si04 IfeO or 
Dimetasilicic acid is 21*28103- EfeO or 
Tnmetasilicic acid is 31128103 EfeO or 



The compounds containing more than one silicon atom in the molecule 
are known as polysilicates The salts of metasilicic acid are meta- 
sihcates 

Many attempts have been made to discover the chemical structure 
of the comparatively simple silicates and several proposals have been 
offered to explain the great differences often observed in the properties 
of silicates with the same empirical formula, but no explanation of these 
differences has thus far proved satisfactory The silicates are so very 
stable under laboratory conditions, and, when they are decomposed, 
their decomposition products are so difficult to study, that it has been 
impossible to determine their molecular volumes or to understand their 
substitution products We are thus driven to ascribe many of the 
anomalies in their composition to solid solutions, to absorption phenom- 
ena, and to the isomorphous mixing of compounds, some of which do 
not exist independently 

There are many silicates, moreover, which cannot be assigned to any 
of the simple acids mentioned above, but which probably must be 
regarded as salts of very much more complex acids Others are pos- 
sible salts of alurninosiliac acids in which aluminium functions in the 
acid portions Thus, albite is usually regarded as a trisilicate, NaAlSisOg, 
and anorthite as an orthosihcate, CaAl2(Si04)2 But the two substances 
are completely isomorphous, and for this reason it is thought that they 
must be salts of the same acid If we assume an aluminosilicic acid of 
the formula HsAlS^Og, albite may be written (NaSi) AlSi2Og, and anor- 
thite (CaAl)AlSi20g The two minerals thus become salts of the same 
acid and their complete isomorphism is explained The relations that 
exist among many silicates might be better understood on the assump- 
tion that they are salts of complex silicic and of aluminosilicic acids 
than on the assumption that they are salts of simpler acids, as is now the 
case But, since it has been impossible to isolate the acids and study 
them we are not certain as to their character It is, therefore, believed 
best to represent most silicates as salts of the simplest acids possible, 
consistent with their empirical compositions as determined by analyses 



302 DESCRIPTIVE MINERALOGY 

As in,the case of salts of other acids there are silicates that contain 
hydrogen and oxygen m such relations to their other components that 
when heated they yield water In some cases this water is driven off at 
a comparatively low temperature and the residue of the compound re- 
mams unchanged A compound of this kind is usually called a hydrate 
or the compound is said to contain water of crystallization In other 
cases a high temperature is necessary to drive off water, and the com- 
pound breaks up into simpler ones In these instances the water is 
said to be combined The compound is usually basic 

In the descriptions of the silicates the order in which the minerals are 
discussed is that of increasing acidity, i e , increasing proportion of the 
Si02 group present m the molecule This order, however, is not fol- 
lowed ngorously The members of well defined groups of closely related 
minerals are discussed together even if their acidity varies widely 
Nearly all the silicates are transparent or translucent and all are elec- 
trical insulators 

THE ANHYDROUS ORTHOSILICATES 

NORMAL ORTHOSILICATES R 4 SiO 4 
OLIVINE GROUP (R"aSi0 4 ) R"=Mg, Fe, Mn, Zn 

The members of the olivine group are normal silicates of the metals 
Mg, Fe, Mn and Zn They constitute an isomorphous series crystalliz- 
ing in the holohedral division of the orthorhombic system (rhombic bi- 
pyramidal class) The most common member is the magnesium-iron 
compound (Mg Fe)2Si04, ohmne, or thrysot Ic, from which the group 
gets its name. The members with the simplest composition are for- 
st&rite (Mg2Si04), fayahte (FeaSiO^ and tephrotte (Mn 2 SiOj.) The 
others are isomorphous mixtures of these, with the exception of three 
rare minerals, of which one, monttcelhte, is a calcium magnesium silicate, 
another, tttanohwne, contains Ti in place of a part of the Si, and the 
other, roeppente, contains some Zn2Si04 Most of them are formed 
by crystallization from molten magmas 

Crystals of all the members of the group are prismatic and all have 
nearly the same habit They are often flattened parallel to one of the 
pinacoids, oo P 56 (oio) or oo P 55 (100) The axial ratios of the com- 
moner members are as follows 

Forstente a : b . c= 4666 : i : 5868 The angle iioAiTo=$o 2' 

Ohvine = 4658 i : 5865 The angle no A 110=49 57' 

Tephroite = 4600 . i : 5939 The angle no A 110=49 2 4' 

Fayahte = 4584 : i : 5793 The angle iioAiTo=49 







ANHYDROUS ORTHOSILICATES 



303 



Crystals of olivine are usually combinations of some or all of the following 
forms- oo P 56 (100), oo P 06 (oio), 
oP(ooi), ooP(no), ooP2(i2o), 

Po6 (Oil), 2Po6(o2l), Poo(lOl), 

P(ni) and 2P2(i2i) (Fig. 163) 
The crystals of fayahte are usually 
more tabular than those of olivine, 
but forsterite and tephroite crystals 
have nearly the same forms The 
cleavage of all is distinct parallel 
to oo P 66 (oio), less distinct parallel 
to oo P oo (100) in olivine, and par- 
allel to oP(ooi) in fayahte 

The compositions of the pure Mg, 
Mn, and Fe molecules are 




FIG 



163 Olivine Crystals with 
ooP, no (m) t oop So, oio (b), 

OP, 001 (c), 2P5,02l(&), 00 PI, 

120 ($),P oo , ioi (d) and P, in (e) 



MgO 
MnO 
FeO 
SiO 2 



Mg 2 Si0 4 Mn 2 Si0 4 

57 i 

70 25 



42 9 



29 75 



Fe 2 Si0 4 



70 6 
29 4 



All natural crystals, however, contain some of all the metals indicated 
and, in addition, many specimens contain also a determmable quantity 
of CaO and traces of other elements 



Forsterite, Olivine and Fayalite (MfeSiO* - (Mg Fe) 2 Si0 4 -Fe 2 Si0 4 ) 

The composition of olivine naturally depends upon the proportion 
of the forsterite and fayahte molecules present in it When the propor- 
tion of FeO exceeds 24 per cent, the variety is known as hya^derite 
A few typical analyses are quoted below 



MgO 


FeO 


CaO 


I 51 64 


S i 


r 08 


II 50 27 


8 S 4 




III 48 12 


ii 18 


12 


IV 39 68 


22 54 





A1 2 3 Si0 2 

42 42 30 

41 19 

40 39 

37 17 



Total Sp Gr 
100 45 3 261 

IOO OO 

99 81 3.294 
99 39 



I From masses enclosed m Vesuvian lava 
II Concretion in basalt near Sasbach, Kaiserstuhl 

III Grams from glacial debris, Jan Mayen, Greenland 

IV Grams from coarse-grained rock, near Montreal, Canada 



304 DESCRIPTIVE MINERALOGY 

In addition, there are often also present small quantities of Ni, Mn, 
and Ti 

Forsterite, olivme and fayalite are usually yellow or green in color 
and have a vitreous luster. Forsterite is sometimes white and ohvine 
often brown. All three minerals become brown or black on exposure 
to the air All are transparent or translucent Their streak is colorless 
or yellow The fracture of ohvine is conchoidal In the other two 
minerals it is uneven Their hardness, density and refractive indices 
for yellow light are as follows 

Hardness Sp Gr a. ft 7 

Forsterite 6-7 3 21-3 33 i 6319 i 6519 i 6698 

Olivme. 6 5-7 3 27-3 37 i 6674 i 6862 i 7053 

Fayalite 65 4 00-4 14 i 8236 i 8642 i 8736 

Before the blowpipe most olivines and forsterites whiten but are in- 
fusible Their fusion temperatures are between 1300 and 1450, 
decreasing with increase in iron Fayahte and varieties of ohvine rich 
in iron fuse to a black magnetic globule All three minerals are decom- 
posed by hydrochloric and sulphuric acids with the separation of gelat- 
inous silica , the iron-rich vaneties are decomposed more easily than 
those poor m iron 

The minerals are characterized by their color and solubility m 
acids. 

Both fayalite and ohvine alter on exposure to the air, the former 
changing to an opaque mixture of Fe20s and Si02, or to the fibrous 
mineral anthophylhte ((Mg-Fe)SiOs), and ohvine to a mixture of 
iron oxides and fibrous or scaly gray or green serpentine (BUMgaS^Oo). 
In other cases, under metamorphic conditions, the alteration is to a 
red lamellar mineral (iddingsite) which may be a form of serpentine, 
or to magnesite, or to the silicate, talc Other kinds of alteration of 
this mineral have also been noted but those descnbed are the most 
common 

Syntheses The members of the ohvine series have been produced 
by fusing together the proper constituents in the presence of magnesium 
and other chlorides They are, moreover, present in many furnace 
slags where they have been made in the process of ore smelting. 

Occurrence Ohvine occurs as an original constituent of basic igneous 
rocks and as a metamorphic product m dolomitic limestones It is 
found also in the form of rounded grains in some meteoric irons. Fayalite 
occurs in acid igneous rocks, especially where affected by pneumatolytic 



ANHYDROUS ORTHOSILICATES 305 

action, and forsterite in dolomitic rocks \\hen they have been meta- 
morphosed by the action of igneous rocks 

Local^t^es Members of the olivine group occur m the basaltic lavas 
of many volcanoes as those of the Sandwich Islands, in the limestone 
inclusions in the lava of Mt Somma, near Naples; in vanous basic 
rocks in Vermont and New Hampshire and at Webster, N C. At the 
latter place granular aggregates of almost pure ohvme constitute great 
rock masses known as dunite 

Fayalite is found in the rhyohtes of Mexico, the Yellowstone Park 
and elsewhere, and in coarse granite at Rockport, Mass , and in the 
Mourne Mountains, Ireland 

Forstente occurs in limestone enclosures in the lava of Mt Somma 
and at limestone contacts with igneous rocks at Bolton, Roxbury, and 
Littleton, Mass , and elsewhere. 

Uses and Production. The only member of the group that is of any 
economic importance is a pale yellowish green transparent ohvine, which 
is used as jewelry under the name of " peridot " Gem material is found 
at Fort Defiance and Rice, in Arizona, scattered loose in the soil The 
little grams came from a basic volcanic rock. The amount produced in 
the United States during 1912 was valued at about $8,100. 

Tephroite (Mn 2 Si0 4 ) 

Although tephroite is regarded as the manganese silicate it nearly 
always contains some of the forsterite molecule 

Analyses of brown (I), and red (II), varieties from Sterling Hill 
gave 

MnO FeO MgO CaO ZnO Loss SiOs Total 

I 52 3* i 52 7 73 * fc> 5 93 28 30 55 99 93 

II 47 62 23 14 03 S4 4 77 35 3* 73 99 2 7 

The mineral is gray, brown or rose-colored and transparent or 
translucent Its streak is nearly colorless It is rarely found m crys- 
tals Its hardness is about 6 and its density 408 It is strongly 
pleochroic in reddish, brownish red and greenish blue tints Its inter- 
mediate refractive index for yellow light = about i 80. 

It is fusible with difficulty (fusing temperature =1200), and is sol- 
uble in HC1 with separation of gelatinous silica It is distinguishable 
from other like-appearing minerals by its difficult fusibility and its 
reaction with HC1 

Syntheses Crystals of the mineral have been made by fusing to- 
gether Si02 and Mn02 in the proportion of i : 2, and by long-continued 



306 DESCRIPTIVE MINERALOGY 

heating of MnCb and Si02 in an atmosphere of moist hydrogen or carbon 
dioxide 

Localities -Tephroite occurs at Mine Hill and Sterling Hill, near 
Franklin, N J , where it is associated with franldmite, zmcite and 
troostite It is found also at Pajsberg in Sweden with other man- 
ganese minerals and magnetite, and at Langban, in Wermland, 
Sweden 

Uses The mineral is of little commercial value It is separated 
with other manganese minerals from the zinc ore of Franklin, N. J , and 
is smelted with these in the production of spiegeleisen, 

WILLEMITE GROUP CVSiQO R"=Zn, Mn 

The willemite group comprises the two minerals willemite (Z^SiO*) 
and troostite ((Zn Mn)2SiC>4), of which the latter is rare Willemite 
occurs in small quantity only, but troostite is an important source of 
zinc at the Franklin locality in New Jersey Both minerals are found in 
crystals 

Willemite and troostite crystallize m the rhombohedral hemihedral 
division of the hexagonal system (ditrigonal scalenohedral class), with 
the axial ratios 

Willemite a ; c= i : o 6698 
Troostite = i . 0.6698 

Willemite and Troostite (Zn 2 SiO 4 -(Zn Mn) 2 SiO 4 ) 

Willemite and troostite occur massive, in grains, and m simple crys- 
tals 

The theoretical composition of willemite is 81022704 and ZnO 
= 72 96, but nearly all natural crystals contain traces of other elements 
When a noticeable quantity of manganese is present, the compound 
is troostite Several analyses are quoted below 

Si02 ZnO MnO FeO Total 

Willemite from Stolberg, Germany 26 90 72 91 35 100 16 

Willemite from Greenland 27 86 71 51 . 37 99 74 

White troostite from Franklin, N J 27 20 65 82 6 97 23 100 22 

Dark red troostite from Franklin, N J 27 14 64 38 6 30 i 24 99,00" 

The crystals of willemite exhibit the forms ooR(ioTo), oop2(ii2o), 
oR(oooi),|R(3034) and -|R(oil2)(Fig 164). Twins, with$P2(3 3 6 10) 
as the twinning planes, are rare The crystals of troostite are even 
more simple, with oop2(ii2o) and R(ioli), usually the only forms 



ANHYDROUS ORTHOSILICATES 307 

present, though -JR(oiT2), -^(0332) and R 3 (2i3i) are also occa- 
sionally found The angle ion A 1101 = 63 59' The cleavage of 
willemite is distinct parallel to oP(oooi), and of troostite distinct 
parallel to ooP2(ii2o), and less perfect parallel to R(ioTi) and 
cR(oooi) 

Willemite is colorless, yellow, brown or blue Troostite is green, 
yellow, brown or gray The colored varieties of both minerals are 
translucent Colorless willemite is transparent Both minerals are 
vitreous in luster Their hardness is between 
5 and 6 and density between 3 9 and 4 3 The 
refractive indices of willemite for yellow light 
are w=i 6931, e=i 7118 

Both minerals glow when heated before the 
blowpipe and are fused with difficulty (about 
1484), and both gelatinize with HC1 Willem- 
ite gives the reaction for zinc with Co(NOa)2 
on charcoal, and troostite gives, in addition, 
the reaction for manganese. FIG 164 Willemite Ciys- 

Syntkeses Willemite crystals have been' td with -Pa, XMO (c), 




made by the action of gaseous hydrofluo- W and ~ 



silicic acid upon zinc, and by the action of 

silicon fluoride on zmc oxide at cherry-red temperature 

Localities and Origin Willemite occurs in comparatively small quan- 
tity at only a few places, associated with other zinc minerals. In 
America it is found in colorless and black crystals at the Merritt 
Mine near Socorro, New Mexico, associated with mimetite, wulfenite, 
cerussite, bante and quartz 

Troostite occurs only at Sterling Hill and Franklin Furnace, N J , 
but in such large quantity that it constitutes an important proportion 
of the zmc ore for which these localities are noted It is associated with 
franklmite and zincite. Both willemite and troostite are results of 
magmatic processes. 

Phenacite (Be 2 Si(>4) 

The theoretical composition of the compound B^SiO* is SiO4= 54 47, 
BeO=45 S3 Many of the analyses of phenacite show that it ap- 
proaches very closely to this. A specimen from Durango, Mexico, for 
example, is: 

SiO= 54 71, BeO=45 32, MgO+CaO= 14- Total- 100 17. 




308 DESCRIPTIVE MINERALOGY 

Phenacite crystallizes in the rhombohedral tetartohedral division of 
the hexagonal system with a : c= i i 0661 It occuis m crystals pos- 
sessing many different types of habit and with many different combina- 
tions of forms Perhaps oop 2 (ii2o), ooP(ioTo), R(ioTi), R 3 (2i3i) 
and |R(oil2) are the most common (Fig 165) Interpenetration 

twins are common at some localities The 
cleavage is indistinct parallel to oo P(ioTo) 
The angle loTi A^IOI = 63 24' 

Phenacite is colorless or white or some 
light shade of yellow or pink. It is trans- 
parent or translucent and has a glassy luster 
Its hardness is 7 5, and density about 3 and 
the refractive indices for yellow light are 

FIG ^-Phenacnte Crystal -' 54*, -i 6700 It'a infusible and 

with oo p 2 , 1 1 20 (a), OOP, insoluble in acids When heated with a 

-IPs - - little soda before the blowpipe it affords a 

ioTo (m) and -j-r, 1322 ^^ ^^^ ^ ^^j ^ phosphores _ 

cent and pyroelectric 

Colorless phenacite resembles quartz and Jerdente, and the yellow 
vanety topaz It is best distinguished from them by its crystalliza- 
tion 

Syntheses Small crystals have been made by the fusion of a mix- 
ture of Si02 and beryllium oxide and borax, and by melting together 
beryllium nitrate, silica and ammonium nitrate 

Localities. Phenacite occurs at the Emerald Mines near Ekaterin- 
burg in the Urals, near Fremont, in the Vogesen, at Reckmgen, in 
Switzerland, in Durango, Mexico, near Pike's Peak, at Topaz Butte, 
and at Mount Aratero, in Colorado, and at Greenwood, m Maine. In 
all cases the mineral is probably a result of pneumatolysis 

Uses. The colorless phenacite is used to a slight extent as a gem 

GARNET GROUP 
(R"3R"' 2 (Si0 4 ) 8 ) R"=Ca, Mg, Fe, Mn R'"=Al, Fe, Cr 

The garnet group comprises a large number of isomorphous com- 
pounds, some of which are very common The members nearly all 
occur in distinct crystals that are combinations of isometric holohedrons 
(hexoctahedral class) Many different names have been given to the 
garnets and analyses show that they possess very different compositions 
With the exception of a few rare varieties, they can all, however, be 
explained as consisting of one of the six molecules indicated below, or of 



ANHYDROUS ORTHOSILICATES 309 

mixtures of them The six molecules and the names of the garnets 
corresponding to them, together with their densities, are. 

Caa Ala (8104)3 Grossulante or Hessomte Sp gr =3 4-3 6 

Mg 3 Al 2 (Si04)3 Pyrope =37-38 

MnaAk (8104)3 Spessattite ==41-43 

Almandite =4 1-4.3 

4)3 Andradite or Melamte =3 8-4 i 

3 Uvarovite =34 



The following table contains the calculated percentage composition 
of the several pure garnet molecules and the records of analyses of some 
typical varieties of the mineral 



SiOs A1 2 O 3 FcfcOs Cr 2 3 FeO MgO CaO MnO TiCfe Total 

I a 40 01 22 69 37 30 100 oo 

Ib 42 01 17 76 5 06 13 35 01 20 100 17 

II a 44 78 25 40 29 82 100 oo 

lib 40 92 22 45 5 46 8 ii 17 85 5 04 46 100 39 

Ilia 36 30 20 75 . 42 95 100 oo 

Illb 36 34 12 63 4 57 47 I 49 44 20 99 70 

IV a 36 15 20 51 43 34 100 oo 

IVb 37 61 22 70 33 83 3 61 i 44 i 12 100 31 

V a 35 45 3i 49 33 06 100 oo 

Vb 35 09 tr 29 15 2 49 24 32 80 36 100 48 

V c 26 36 22 oo i 25 30 72 tr, 21 56 101 89 

Via 38 23 29 27 29 27 100 oo 

VIb 36 93 5 68 i 96 21 84 i 54 31 63 99 58 

I a Theoretical composition of the grossulante molecule 

Ib Green and red grossulante from the limestone at Santa Clara, Cal. 

II a Theoretical composition of the pure pyrope molecule 

lib Pyrope from a pendotite in Elliot Co , Ky Also, HzO = 10. 

Ilia Theoretical composition of spessartite 

Illb Spessartite from Amelia Court House, Va 

IV a Theoretical composition of almandite 

IVb Almandite from Sahda, Colo 

V a Theoretical composition of andradite 

Vb Andradite from East Rock, New Haven, Conn Also, HaO.35. 

V c Schorlomite from Magnet Cove, Ark 

VI ft Theoretical composition of uvarovite 

VIb Uvarovite from Bissersk, Urals 

The crystals of garnet are usually simple combinations of oo 0(no) 
(Fig. 166); 202(211) and often 301(321) (Figs 167 and 168), although 
all the other holohedrons are also occasionally met with. Their cleavage 
which is indistinct is parallel to oo 0(no). 



310 



DESCRIPTIVE MINERALOGY 



When examined in polarized light many garnets, especially those 
occurring in metamorphic rocks, are doubly refracting and, therefore, 
have not the molecular structure belonging to isometric crystals This 




FIG 166 Garnet Crystal. (Natural size ) Form ooQ (no) 





FIG 167 FIG 168. 

FIG 167 Garnet Crystals with coO, no (d) and 202, 211 (), 
FIG 168 Garnet Crystal with d and n as in Fig 167 Also oo 02, 210 (<?) and 308 

231 (s) ' 

phenomenon has been explained as due to several causes, the most rea- 
sonable explanation ascribing it to strains produced in the crystals upon 
cooling 



ANHYDROUS ORTHOSILICATES 311 

The garnets vary in color according to their composition, the com- 
monest color being reddish brovin Their luster is Mtreous, their 
streak white, hardness 6-7 5, and density 3 4-4 3 They are transparent 
or translucent Most varieties are easily fusible to a light brown or 
black glass, -which in the case of the varieties rich in iron is magnetic 
U\ arovite, however, is almost infusible Some garnets are unattacked 
by acids, others are partially decomposed 

Garnets, when in crystals, are easily distinguished from other sim- 
ilarly crystallizing substances by their color and hardness Massive 
garnet may resemble tcsuuant'e, spkene, zircon or tzunnaine It is 
distinguished from zircon by its easier fusibility and from vesuviarnte 
by its more difficult fusibility, from tourmaline by its higher specific 
gravity, and from sphene by the reaction from titanium 

Under the influence of the air and moisture garnets may be partially 
or entirely changed to epidote, muscovite, chlorite, serpentine, and oc- 
casionally to other substances 

Grossularite, Essomte, Hessonite, or Cinnamon Garnet occurs 
principally in crystalline schists and in metamorphosed limestones, 
where it is associated with other calcium silicates It is found also 
in quartz ve;ns The mineral is white, bnght yellow, cinnamon-brown 
or some pale shade of green or red. The lighter-colored varieties are 
transparent or nearly so Those that are colored are used as gems 
Much of the hyacvnfi of the jewelers is a red grossulante (seep 317) 
Its hardness is about 7 and its density 3 4-3 6 It is fairly easily 
fusible before the blowpipe. The refractive index of colorless vari- 
eties for yellow light is, n= i 7438 

Good crystals of grossulante occur at Phippsburg, Raymond and 
Rumf ord, in Maine, and at many other places both in this country and 
abroad Bright yellow varieties are reported from Canyon City, Colo 

Pyrope is deep red, sometimes nearly black. Its hardness is a little 
greater than 7 and its density 3 7 Its refractive index for yellow light 
is between i 7412 and i 7504 The pure magnesium garnet is unknown 
All pyropes contain admixtures of iron and calcium molecules Many 
pyropes are transparent Those with a dark red color are used as gems 
They occur principally in basic igneous rocks 

The principal occurrence of the gem variety in this country is in 
Utah, near the Arizona line, about 100 miles west of Ganado, Ariz , 
where it is found lying loose m wind-blown sand 

Rhodolite is a pale rose-red or purple variety from Macon Co., N C 
It consists of two parts pyrope and one of almandite. 



312 DESCRIPTIVE MINERALOGY 

Spessartite is hyacinth or brownish red, with occasionally a tinge 
of violet The purest varieties are yellow, but since there is nearly 
always an admixture of one of the iron molecules, the more usual color 
is reddish brown The mineral is usually transparent Its hardness is 
7 or a little greater, and its density 3 77-4 27 Its refractive index for 
yellow light is i 8105 In the blowpipe flame it fuses fairly easily to a 
black, nonmagnetic mass, and with borax gives an amethyst bead It 
is found in acid igneous rocks and in various schists 

Its best known occurrences in the United States are IP granite, at 
Haddam, Conn , in pegmatite, at Amelia Court House, Va , and in 
the lithophyse of rhyohtes, near Nathrop, in Colorado 

Almandite is deep red, brownish red or black It is one of the com- 
monest of all garnets It furnishes nearly all the material manufactured 
into abrasives Transparent vaneties are also used as gems The min- 
eral has a hardness of 7 and over Its density is 4 1-4 3, and its refrac- 
tive index, n, for yellow light, is about i 8100 It is slightly decom- 
posed by HC1 Before the blowpipe it fuses to a dark gray or black 
magnetic mass It is found in granites and andesites, and also in various 
gneisses and schists and in ore veins 

Its best known occurrences in North America are at Yonkers and 
at various points in the Adirondacks, N Y , at Avondale, Pa , and on the 
Stickeen River, in Alaska 

Andradite, or meknite, is black, brown, brownish red, green, brown- 
ish yellow or topaz-yellow. The purest varieties are topaz-yellow or 
light green and transparent The former constitute the gem topawhte 
and the latter, demantwd The black variety, melamte, nearly always 
contains titanium It occurs m alkaline igneous rocks, in serpentine, 
in crystalline schists and in iron ores The most titamferous varieties 
are known as schorlomtte The hardness of andradite is about 7 and its 
density between 3 3 and 41 n for yellow light = i 8566 It is fusible 
before the blowpipe to a black magnetic mass 

The mineral is very widely spread It occurs at Franklin, N J , m 
metamorphosed limestone, near Francoma, N H , in quartz veins, and 
at many other places A black titamferous vanety occurs in a meta- 
morphosed limestone in southwestern California and near Magnet Cove, 
m Arkansas The vanety found at Magnet Cove is schorlormte It is a 
black glassy mineral associated with brookite (TiCfe), nephdme (p 314), 
and thomsomte (p 455) 

Common garnet is a mixture of the grossularite, almandite and 



ANHYDROUS ORTHOSILICATES 313 

andradite molecules It occurs in many metamorphosed igneous rocks 
and in some slates 

Uvarovite is emerald-green It is rare, occurring only with chromite 
in serpentine at Bissersk and Kyschtim in the Urals and in the chromite 
mines at Texas, Penn , and New Idria, Cal Its hardness is about 7 
and density 3 42 Its refractive index for yellow light is i 8384 It is 
infusible before the blowpipe but dissolves in borax, producing a green 
bead 

Syntheses Garnet crystals have been produced by fusing 9 parts of 
nephelme and i part of augite (p 374) The fusion results in a 
crystalline mass of nephelme, in which spinel and melamte crystals are 
embedded 

Occurrence The members of the garnet group are widely spread in 
nature They occur in schists, slates and other regionally metamor- 
phosed rocks, in granite, rhyohte and other igneous rocks, and as con- 
tact products in limestones They are found also in quartz veins, in 
pegmatite, and associated with other silicates in ore veins. In some 
instances they separated from a cooling magma, in others they are the 
products of pneumatohtic process, and in others they are the results of 
contact and dynamic metamorphism 

Uses and Production The varieties that are transparent are used 
as gems Other varieties are crushed and employed as abrasives The 
value of the gem material produced in the United States in 1912 was 
$860 The production for abrasive purposes was 4,182 short tons, val- 
ued at $137,800 All of this was produced in the mountain regions of 
New York, New Hampshire and North Carolina The rock is crushed 
and the garnet separated by hand picking, screening, or by jigging 
The crushed material is used largely in the manufacture of garnet paper 

NEPHELINE GROUP 

The nephelme group of minerals includes three closely related com- 
pounds, of which nepheline is the most common They are all alumino- 
silicates of the alkalies Nephelme appears to be a solution of Si02, 
or of albite, in isomorphous mixtures of the orthosilicates, NaAlSiO 
and KAlSiO* in the proportion of 8 molecules of the silicates to one of 
Si02, thus 

8(Na K)AlSi04+Si0 2 =(Na K) ((Na- K) AlSi0 3 )2Al 6 (Si04) 7 

The other two members of the group are eucryptite (LiAlSKX) and 
kdhopkOOe (KAlSiQ*). 



314 DESCRIPTIVE MINERALOGY 

The members of the group crystallize in the hexagonal system and 
are apparently holohedral, but nephelme is hemihedral and hemi- 
morpmc (hexagonal pyramidal class) At temperatures above 1,248 
the nephelme molecule crystallizes also in the trichmc system as car- 
negieite (see p. 418), 



Nephelme 

Although approximately a potash-soda silicate, nearly all specimens 
of nephelme contain more or less CaO and nearly all contain small 
quantities of water All contain an excess of SiCte To avoid the 
necessity of assuming the existence of this SiCb m solution with 
(Na K)AlSi04, it has been suggested that the variable composition of 
the mineral may be explained by regarding it as a solid solution of 
NaAlSisOg and CaAkS^Os (best known in their trichmc forms as 
albite and anorthtte) in an isomorphous mixture of the two molecules, 
NaAlSi04 and KAlSiO* The average of five analyses of crystals from 
Monte Somma, Italy, is shown in I, and the composition of a mass of 
the mineral from Litchfield, Maine, in II 



Si0 2 A1 2 03 CaO MgO Na 2 KaO H 2 Total 

I 44 08 33 28 i 57 19 16 oo 4 76 15 100 03 

II 43 74 34 48 tr tr 16 62 4 55 86 100 25 

When found in crystals, the mineral is apparently holohedral in form 
with an axial ratio i 8389 The crystals are nearly always short 
columnar in habit and usually consist of very 
simple combinations The most prominent 
forms are ooP(ioTo), oop2(ii2o), oP(oooi), 

2P(202l), P(lo7l), |P(loT2) and 2P2(lI2l) 

(Fig 169) Their cleavage is imperfect parallel 
toooP(ioIo) and oP(oooi) 

Nephelme is glassy, white or gray and trans- 
parent, when occurnng as implanted crystals 
FIG i6 9 --NepheUneCrys- The translucent va *y with a glassy luster 
tal with oP, oooi (c), *^ a * occurs ln rocks is known as eleohte This 
oo p, iolo (), P, loir variety may be gray, pink, brown, yellowish or 
(p) andoop 2 , 1120 (a) greenish The streak is always white The 
fracture of both forms is conchoidal or uneven; 
hardness, 5-6 and density, 2 6 For yellow light, co= 1.5424, = i 5375. 



ANHYDROUS ORTHOSILICATES 315 

Before the blowpipe nephelme melts to a \\hite or colorless blebby 
glass At 1,248 it passes over into carnegieite \\hich melts at 1,526 
It dissolves in hydrochloric acid with the production of gelatinous 
silica Its powder before and after roasting reacts alkaline 

The mineral is distinguished from other silicates by its crystalliza- 
tion, gelatinization with acids, and hardness The massive varieties 
are often distinguishable by their greasy luster 

Nephelme alters to various hydrated compounds, especially to the 
zeolites (p. 445), and to gibbsite, muscovite, cancnmte and sodahte 

Syntheses Nephelme has been prepared by fusing together AfeOa, 
SiO2 and Na 2 C03, and by the treatment of muscovite by potassium 
hydroxide. 

Occurrence The mineral occurs principally as an original constit- 
uent of many igneous rocks, both plutomc and volcanic, and also as 
crystals on walls of cavities in them 

Locates Crystals occur near Eberbach, in Baden, in the inclu- 
sions within volcanic rocks at Lake Laach, in Rhenish Prussia, in the 
older lavas of Monte Somma, Naples, Italy, at Capo de Bove, near 
Rome, in southern Norway, and at various other points in southern 
Europe Massive forms are found m coarse-brained rocks near Litch- 
field, Maine, Red Hill, N H , Magnet Cove, Ark., m the Crazy Mts , 
Mont , and at other places 



Cancrinite 

Cancnmte is extremely complex in composition It is nearly allied 
to nephelme but contains a notable quantity of C0 2 It corresponds 
approximately to an hydrated admixture of Na 2 COs and 3NaAlSi04, 
in which some of the Na is replaced by K and Ca Specimens from 
Barkevik (I) in Norway, and from Litchfield (II), in Maine, yield the 
following analyses: 



Si0 2 AkOs Fe 2 3 CaO Na 2 K 2 O C0 2 EfeO Total 
I 37 01 26 42 7 19 18 36 7 27 3 12 99 37 

II. 36 29 30 12 tr. .4 27 19 56 18 6 96 2 98 100 36 

Cancrinite is hexagonal (dihexagonal bipyramidal class). 

Crystals are rare, and those that do exist are very simple, prismatic 
forms bounded by ooP(ioTo), ooF2(ii2o), oP(oooi) and P(ioTi) 
Their axial ratio is i : 4410 



316 DESCRIPTIVE MINERALOGY 

The mineral is usually found without crystal planes It is colorless, 
white or some light shade, such as rose, bluish gray or yellow Its 
streak is \vmte, its luster glassy, greasy or pearly and it is translucent 
Its cleavage is perfect parallel to ooP(ioTo) and less perfect parallel 
to oo P 2 1 1 20) Its break is uneven, hardness 5 and density 245 
For red light* u>=i 5244? *=i 49S5 

Before the blowpipe the mineral loses its color, swells and fuses to a 
colorless blebby glass In the closed glass tube it loses CCb and water, 
and becomes opaque After roasting it is easily attacked by weak 
acids with effervescence and the production of gelatinous silica When 
boiled with water Na2COs is extracted in sufficient quantity to give an 
alkaline reaction 

Cancrimte is easily distinguished by its effervescence with acids and 
the production of gelatinous silica 

Synthesis Small colorless, hexagonal crystals with a composition 
corresponding to that of cancnmte, have been made by treating mus- 
covite with a solution of NaOH and NasCOs at 500 

Occurrence The mineral occurs principally as an associate of neph- 
elme in certain coarse-grained igneous rocks In some cases it appears 
to be an original rock constituent and in others an alteration product of 
nephelme It sometimes alters to natrohte (see p 454), foiming pseu- 
domorphs 

Localities Cancrimte is found in rocks at Ditro, Hungary, at 
Barkevik and other localities in southern Norway, where it occurs m 
pegmatite dikes, m the parish of Kuolajarvi, in Finland, and in nephelme 
syenite at Litchfield m Maine, 

ZIRCON GROUP 

The orthosihcates of zirconium, zircon, and of thorium, thorite, con- 
stitute a group, the members of which possess forms that are almost 
identical with those of rutile, cassitente and xenotime Indeed, parallel 
growths of zircon and xenotime are not uncommon. Formerly zircon 
was grouped with the two oxides. 

Zircon and thorite are tetragonal (ditetragonal bipyramidal class), 
with approximately the same axial ratios and the same pyramidal angles. 
The two minerals are completely isomorphous 

Zircon ZrSiO* a ' c= 6391 in A ill = 56 37', 
Thorite ThSi0 4 =6402 =56 40'. 

Zircon is fairly common Thorite is rare. 



ANHYDROUS ORTHOSILICATES 



317 



Zircon (ZrSiO 4 ) 

Zircon, like rutile, is a fairly common compound of a comparatively 
rare metal It is practically the only ore of the metal zirconium. It is 
found mainly in crystals and as gravel 

Although some specimens of zircon contain a large number of ele- 
ments, others consist only of zirconium, silicon and oxygen in propor- 
tions that correspond to the formula ZrSiO*, which demands 67 2 per 
cent ZrO and 32 8 per cent SiOg 

Its axial ratio is a : r=i ' 6301 Its crystals are usually simple 
combinations of o P(uo) and P(m), with the addition of oo P oo (100) 






FIG 170 



PIG 171 



FIG. 170 Zircon Crystals with P, no (w), ooPoo, 100 (a), 3?, 331 (}, 

P, in (p) andsPs, 311 (x) 
FIG 171 Zircon Twinned about P < (101) =2P (221) 

and often 3P3(3ii) (Fig 170) Elbow twins, like those of rutile and 
cassitente, are known (Fig 171) 

The cleavage of zircon is very indistinct. Its fracture is conchoidal. 
Its hardness is 7.5 and density about 4 7 The mineral varies in tint 
from colorless, through yellowish brown to reddish brown Its streak 
is uncolored and luster adamantine Most varieties are opaque, but 
transparent varieties are not uncommon The orange, brown and red- 
dish transparent kinds constitute the gem known as hyacinth The 
refractive indices for yellow light are* o>=i 9302, 6=1,9832. 

Zircon is infusible, though colored varieties often lose their color 
when strongly heated In the borax and other beads the mineral gives 
no preceptible reactions. In fine powder it is decomposed by concen- 
trated sulphuric acid. When fused with sodium carbonate on platinum 
it is likewise decomposed, and the solution formed by dissolving the 
fused mixture in dilute hydrochloric acid turns turmeric paper orange. 
This is a characteristic test for the zirconium salts. 



318 DESCRIPTIVE MINERALOGY 

The mineral is easily recognized by its hardness, its resistance toward 
reagents and its crystallization 

Syntheses Small crystals of zircon are obtained by heating for sev- 
eral hours in a steam-tight platinum crucible a mixture of gelatinous 
silica and gelatinous zirconium hydroxide Crystals have also been, 
made by heating for a month a mixture of ZnCb and SiOa with 6 times 
their weight of lithium bimolybdate 

Occurrence and Ongin Zircon is widely spread in tiny crystals as a 
primary constituent in many rocks, and in large crystals in a few, notably 
in limestone and a granite-like rock known as nephelme syenite In 
limestone it is a product of contact action. It occurs also in sands, 
more particularly in those of gold regions, and abundantly in a sand- 
stone near Ashland, Va 

Localities The principal occurrences of the mineral are Ceylon, the 
home of the gem hyacinth, the gold sands of Australia, Arendal, 
Hakedal and other places in Norway; Litchfield and other points in 
Maine, Diana, m Lewis Co , and a large number of other places in New 
York, at Reading, Penn , Henderson and other Counties, m North 
Carolina and Templeton, Ottawa Co , Quebec 

Uses. Zircon is the principal source of the zirconium oxide emplo)'ed 
in the manufacture of gauze used in incandescent gas lights and in the 
manufacture of cylinders for use in procuring a light from the oxyhydro- 
gen jet. The mineral has been mined for these purposes in Henderson 
Co , North Carolina 

Transparent orange-colored zircons are sometimes used as gems 
since they possess a high index of refraction and consequently have 
a great deal of " fire " These are the true hyacinth The mineral 
often called by this name among the jewelers is a yellowish brown 
garnet 

Production k small quantity of zircon is usually obtained from 
Henderson Co., N C , but it rarely amounts to more than a few hundred 
pounds. The mineral occurs in a pegmatite and the soil overlying its 
outcrop. It is obtained by crushing the rock and hand picking Usually 
there is a little also separated from the sands in North Carolina and 
South Carolina that are washed for monazite. A pegmatite dike, rich 
in zircon, is also bemg prospected in the Wichita Mountains, Okla,, but 
no mining has yet been attempted. 



ANHYDROUS ORTHOSILICATES 



319 



Thorite (ThSiO 4 ) 

Thorite occurs in simple crystals bounded by ooP(no) and P(in) 
(Fig 172), and in masses The mineral is always 
more or less hydrated, but this is believed to be 
due to partial weathering It is black or orange- 
yellow (prangeite), has a hardness of 5 and a specific 
gravity of 4 5-5 for black vaneties and 5 2-5 4 for 
orange varieties Its streak is brown or light orange 
Hydrated specimens are soluble in hydro chloric acid 
with the production of gelatinous silica The min- 
eral occurs as a constituent of the igneous rock, 
augite-syemte, at several points m the neighborhood 
of the Langesundfjord, Norway, 




FIG 172 Thonte 
Crystal with oc P, 
no (m) and P ; 



BASIC ORTHOSILICATES 
ANDALUSITE GROUP 

Three compounds with the empirical formula AkSiOs exist as min- 
erals, kyamte, or disthene, andalusite and silhmanite. The first named is 
less stable with reference to chemical agents than the other two, but at 
high temperatures both kyamte and andalusite are transformed into 
silhmanite Kyamte is regarded as a metasihcate (AlO^SiOa. The 
other two are thought to be orthosilicates (Al(A10)SiC>4) The latter 
are orthorhombic and both possess nearly equal prismatic angles 
They differ markedly, however, in their optical and other physical 
properties and, therefore, are different substances Kyamte is tnchnic 
For this reason and because of its different composition it is not re- 
garded as a member of the andalusite group A fourth mineral, topaz, 
differs from andalusite in containing fluorine. Often this element is 
present in sufficient quantity to replace all of the oxygen in the radical 
(A1O) In other specimens the place of some of the fluorine is taken 
by hydroxyl (OH). The general formula that represents these varia- 
tions is A1(A1(F OH)2)Si04 The mineral crystallizes in forms that are 
very like those of andalusite, and if corresponding pyramids are selected 
as groundforms their axial ratios are nearly alike. Unfortunately, 
however, different pyramids have been accepted as groundforms, and 
therefore the similarity of the crystallization of the two minerals has 
been somewhat obscured Daribunte, another mineral that crystallizes 
m the orthorhombic system with a habit like that of topaz is often also 
placed in this group, although it is a borosilicate, thus CaB2 (8104)2- 



320 



DESCRIPTIVE MINERALOGY 



If 4P2(24i) be taken as the groundform of andalusite, 3^(331) as 
that of topaz and 3? (331) as that of danbunte, the corresponding axial 
ratios would be 

Andalusite a b . c= 5069 i i 4246 
Topaz = 5281 I * 43*3 

Danbunte = 5445 * * 44 2 

These, however, are not the accepted ratios, since other and more prom- 
inent pyramids have been selected as the groundforms 

Andalusite and Sillimanite (Al(AlO)SiO 4 ) 

Andalusite and sillimamte have the same empirical chemical compo- 
sition and crystallize with the same symmetry, which is orthorhombic 
holohedral (rhombic bipyramidal class), but they have different physical 
properties and different crystal habits, and hence are regarded as dif- 
ferent minerals The theoretical composition of both is 



8102=3702, 



Total= 16000 



Nearly all specimens when analyzed show the presence of small 

quantities of Fe, Mg, and Ca, but otherwise they correspond very closely 

to the theoretical composition 

Both minerals are characteristic of metamorphosed rocks, but 

andalusite occurs principally in those that have been metamorphosed by 

contact with igneous mtru- 
sives, while Sillimanite is 
especially characteristic of 
crystalline schists and, in gen- 
eral, of rocks that were dy- 
namically metamorphosed It 
also occurs with ohvme as in- 
clusions in basalt lavas Silh- 

FIG 173 Andalusite Crystals with oop, no mamte is more stable at high 
(m), oP ooi (c), PS, oii w , cops, TOO temperatures than andalusite 

(6), OOP 00,^010 (a), oo Pa, 210 (/), f^ * 

120 (), Poo, ioi (r), P, in (p) and 

121 (*) 



When m contact rocks it is 
found nearer the intrusive 



than andalusite 

Andalusite The accepted axial ratio of andalusite is 986*1 : i : 7024 
Its crystals are columnar in habit and are usually simple combinations 

Of 00 P 00 (IOO), 00 P 00 (OIO), OP(OOI), 00 P(lio), 00 P2(2IO), 00 P2(l2o) 

Poo (ioi), Poo (on) with sometimes P (in) and 2P2(i2i) (Fig 173). 
The angle no A 110=89 12' 



ANHYDROUS ORTHOSILICATES 321 

The mineral, when fresh, is greenish or reddish and transparent 
Usually, however, it is more or less altered, and is opaque, or, at most, 
translucent, and gray, pink or violet Its cleavage is good parallel to 
oo P(no) and its fracture uneven Its hardness is 7 or a little less and 
its density 3 1-3 2 In some specimens pleochroism is marked, their 
colors being olive-green for the ray vibrating parallel to a, oil-green for 
that vibrating parallel to b and dark red for that vibrating parallel to c 
For yellow light the indices of refraction are 01=16326, 1(3=16390, 
7=1 6440 

Before the blowpipe the mineral gradually changes to sillimamte and 
is infusible When moistened with cobalt nitrate and roasted it becomes 
blue It is insoluble in acids 

The mineral is distinguished by its nearly square cross-section, its 
hardness, its mfusibihty, and the reaction for Al, and by its manner of 
occurrence in schists and metamorphosed slates 

Some specimens contain as inclusions large quantities of a dark 
gray or black material, which may be carbonaceous, arranged m 
such a way as to give a cross-like figure in cross-sections of crystals. 
Because of the shape of the figure exhibited by these crystals, this 
variety was early called chiastohte, and was valued as a sacred 
charm. 

Andalusite alters readily to kaolin (p 404), muscovite (p 355), and 
sillimamte It has not been produced artificially 

Occurrence Andalusite is found principally in clay slates and schists 
that have been metamorphosed by contact with igneous masses, and 
to a less extent m gneisses 

Localities Its principal occurrences are in Andalusia, Spain, at 
Braunsdorf, Saxony, at Gefrees, in the Fichtelgebirge, in Minas 
Geraes, Brazil, and m the United States at Standish, Maine, Westford, 
Mass , and Litchfield, Conn Chiastohte occurs at Lancaster and 
Sterling, Mass 

Use The only use to which andalusite has been put is as a semi- 
precious stone, and for this purpose only the chiastolite variety is of any 
value 

SiUimanite, or fibrokte, occurs principally m acicular or fibrous 
aggregates, on the individuals of which only the prismatic forms 
ooP(no) and oP|(23o) and the macropmacoid ooPw(ioo) can be 
detected End faces are not sufficiently developed to warrant the 
determination of an axial ratio The relative values of the a and b 
axes are 687 : i. The angle iioAiio* 8 ^ . 

While most of the fibers correspond m composition very closely to the 



322 DESCRIPTIVE MINERALOGY 

theoretical value demanded by the formula Al(A10)Si04, many contain 
small quantities of Fe20a, MgO and HkO 

The mineral is yellowish gray, greenish gray, olive-green or brownish 
It has a glassy or greasy luster and when pure is transparent Most 
specimens, however, are translucent, and many of the colored varieties 
show a pleochroism in brown or reddish tints Its cleavage is perfect 
parallel to oo P 55 (100) Its needles have an uneven fracture trans- 
versely to their long directions Their streak is colorless, hardness 
6-7 and density 3 24 The mdices of refraction for the lighter colored 
varieties are a=i 6603, j8= i 6612, 7 i 6818 for yellow light 

Sillimanite reacts similarly to andalusite toward reagents and before 
the blowpipe It is distinguished from other minerals by its habit and 
manner of occurrence. 

This mineral is much more resistant to weathering than is andalusite 
It is, however, occasionally found altered to kaolin On the other hand, 
it is known also in pseudomorphs after corundum 

Synthesis It has been produced b> cooling fused silicate solutions 
rich in aluminium 

Occurrence Sillimanite is very widely spread in schistose rocks, 
especially those that have been formed from sediments It is essentially 
a product of dynamic metamorphism, but is formed also bv contact 
metamorphism, m which case it is found near the intrusive, where the 
temperature was high 

Localities Its principal occurrences in North America are in quartz 
veins cutting gneisses at Chester, Conn , at many points in Delaware 
Co , Penn , and at the Culsagee Mine, Macon Co , N C At the latter 
place and at Media in Penn , a fibrous variety occurs m such large 
masses as to constitute a schist known as fibrohte schist. 

Topaz (Al(Al(F-OH) 2 )Si0 4 ) 

Topaz is a common constituent of many ore veins and is often present 
on the walls of cracks and cavities in volcanic rocks It occurs massive 
and also in distinct and handsome crystals 

The mineral has a varying composition, which is explained in part 
by the fact that it is a mixture of the two molecules Al(AlF2)SiO4 and 
Al(Al(OH)2)SiOi The theoretical composition of the fluorine molecule 
is 8102=32 6, A1 2 03=SS 4, F=2o 7=108 7, deduct (0 = 2F)8 7 
= loo.oo. A specimen from Florissant, Colo , gave. 

F=i6 04=106 20-6 7s(0=F) = 99 45. 



ANHYDROUS ORTHOSILICATES 



323 



Crystals of topaz appear to be orthorhombic (rhombic bipyramidal 
class), but the fact that they are pyroelectnc and that they frequently 
exhibit optical phenomena that are not in accord with the symmetry of 
orthorhombic holohedrons suggests that they may possess a lower grade 
of symmetry On the assumption that the mineral crystallizes with the 
symmetry of orthorhombic holohedrons the axial ratio of fluorine varie- 
ties is 5281 i 4771 l With the increasing presence of OH, however, 
the relative length of a increases and that of c diminishes The angle 
noAiTo=55 43'- 

The crystals are usually prismatic in habit with ooP(no) and 
oo P?(i2o) predominating They are notable for the number of forms 






FIG 174 FIG 175. 

FIG 174 Topaz Crystals with oo P, no (m), oo pT, 120 (Z), P, in (u), 2P, 221 (o) 

4? oo , 041 00 and oo P oo , oio (6) 

FIG 175 Topaz Crystal with m, I, n and y as in Fig 174. Also 2? oo , 021 (/), 
|P oo , 043 (*) and 2P 55 , 201 (d) 

that have been observed on them, especially in the prismatic zone and 
among the brachypyramids The number of the latter that have 
already been identified is about 45 

The three types of crystals that are most common are shown in 
Figs 174, 175 and 176 Their most prominent forms are ooP(no), 
ooP2(i2o), Poo (on), P(ni), |P(223), 4? ^(041), oo PJ (130) and 
oP(ooi). Often planes are absent from one end of the vertical axis, 
but since the etch figures on the prismatic planes do not indicate hemi- 
morphism, the absence of the lacking planes is explained as being due to 
unequal growth The planes of the prismatic zone are usually striated 

The mineral is colorless, honey yellow, yellowish red, rose and rarely 
bluish. When exposed to the sunlight the colored varieties fade, and 



The more commonly accepted axial ratio is a : 6 : c- 
p(22i) 'being taken as the groundfonn* 



5285 : i : .9539, the form 



324 



DESCRIPTIVE MINERALOGY 




fj d, and tt as m Figs 174 and 175 
Also P, 223 (z), oP, ooi (c) and 
4P 55 , 401 (p) 



when intensely heated some honey-yellow crystals turn rose-red Its 
cleavage is perfect parallel to oP(ooi) and imperfect parallel to P 06 (on) 
and P oo (101) The hardness of the mineral is 8 and its density 3 5-3 6 
Its refractive indices for yellow light are a= i 6072, = i 6104, 7= i 6176 
for a variety containing very little OH, and 05=16294, =16308, 

7=16375 for a variety rich m 
hydroxyl The indices of refraction 
being high, the mineral when cut 
exhibits much brilliancy a feature 
which, together with its hardness, 
gives it much of its value as a 
gem. 

Topaz is infusible before the 
blowpipe and is insoluble in acids 

FIG 176 Topaz Crystal with m, I, y, At a high temperature it loses its 

fluorine as silicon and aluminium 
fluorides The mineral also ex- 
hibits pyroelectncal properties, but 
these are apparently distributed without regularity m different 
crystals Many crystals contain inclusions of fluids containing bubbles, 
and sometimes of two immiscible fluids the nature of which has not yet 
been determined It has been thought that the principal fluid present 
is liquid carbon-dioxide or some hydrocarbon 

The mineral is distinguished from yellow quartz by its crystalliza- 
tion, its greater hardness and its easy cleavage 

Topaz is frequently found coated with a micaceous alteration product 
which may be steatite (p 401), muscovite (p 355) or kaolin (p 404) 

Synthesis Crystals have been made by the action of hydrofluosihcic 
acid (EfeSiFe) upon a mixture of silica and alumina m the presence of 
water at a temperature of about 500. 

Occurrence The mineral occurs principally in pegmatites, espe- 
cially those containing cassitente, in gneisses, and in acid volcanic rocks 
In all cases it is probably the result of the escape of fluorine-bearing 
gases from cooling igneous magmas. 

LocalMes Topaz is found in handsome crystals at Schneckenstem 
in Saxony, in a breccia made up of fragments of a tourmalme-quartz 
rock cemented by topaz. It occurs also in the pegmatites of the tin 
mines m Ehrenfnedersdorf, Marienberg and other places in Saxony, 
Bohemia, England, etc , on the walls of cavities in a coarse granite m 
Jekatennburg and the Hmengebirge, Russia, in veins of kaohn cutting 
a talc schist in Mrnas Geraes in Brazil; and in the cassitente-bearmg 



ANHYDROUS ORTHOSILICATES 325 

sands at San Luis Potosi, Durango and other points in Mexico In the 
United States it occurs on the walls of cavities m acid volcanic rocks, at 
Nathrop, Colo , in the Thomas Range, Utah, and other places It occurs 
also in veins Tilth muscovite, fluonte, diaspore and other minerals at 
Stoneham, Maine, and Trumbull, Conn 

Uses and Pi oduction Topaz is used as a gem About 36 Ib , valued 
at $2,675, was produced in the United States in 1911. In the following 
year the production was valued at only $375. 

Danburite (CaB 2 (Si0 4 )2) 

Danbunte, which is a comparatively rare mineral, is a calcium 
borosilicate with the following theoretical composition 8102=4884, 
B2Os = 28 39 and CaO= 2277 Usually, however, there are present in it 
small quantities of AfeOs, Fe20s, MnaOs and EfeO Thus, crystals from 
Russell, New York, contain 

SiO 2 B 2 O 3 Al 2 3 ,etc H 2 CaO Total 

49 70 25 80 i 02 20 23 26 99 98 

The mineral crystallizes in the orthorhombic system (rhombic bipy- 
ramidal class), with an axial ratio 5445 : i 4801 Its crystals are 
usually prismatic in habit They contain a great number of forms, of 
which oo P &> (100), oo P 06 (oio), co P2(i2o), oo P4(i4o), and oo P(iio) 
among the prisms, 2P4(i42), 2P?(i2i) among 
the pyramids and oP(ooi) are the most prom- 
inent (Fig. 177). The angle iioAiib= 
57 8'. 

When fresh and pure the mineral is trans- 
parent, colorless or light yellow, but when 
more or less impure is pink, honey-yellow or 
dark brown Its streak is white, and luster 
vitreous Its cleavage is imperfect parallel to JT IG I77 Danbunte Cr>s- 
oP(ooi) and its fracture uneven or conchoidal tal with oop, no (m), 
Its hardness is about 7 and density 2 95-3 02 p 2, 120 (Z), PSo , 101 

Its refractive indices for vellow light are <,**,* <r)"d4P-, 

041 (w) 
a=l 6317, 0=1 6337, 7=1 6383 

Before the blowpipe the mineral fuses to a colorless glass and colors 
the flame green It is only slightly attacked by hydrochloric acid, but 
after roasting is decomposed with the formation of gelatinous silica. 
It phosphoresces on heating, glowing with a red light. 

Origin Danburite is probably always a product of pneumatolytic 




i 

m 



326 DESCRIPTIVE MINERALOGY 

action, as it is found m quartz and pegmatite veins in the vicinity of 
igneous rocks and on the walls of hollows within them 

Locahtm Its principal occurrences in this country are at Danbury, 
Conn , where it is in a pegmatite, and at Russell, N Y , on the walls of 
rocks and hollows in a granitic rock Its principal foreign occurrence is 
at Piz Valatscha, in Switzerland. 

EPIDOTE GROUP (CfcR'"i(OH)(Si(>4)i) 

The epidote group comprises six substances, of which two are di- 
morphs with the composition Ca 2 Al,3 (OH) (SiO^s = Ca2Al2(A10H) (SiO-Os 
One of these, known as ztnstie, crystallizes in the orthorhombic system, 
and the other, known as dinozoivite, m the monochiuc system The 
other four are isomorphous with clmozoisite These are hancockite, 
epidote, piedmontite and allanite The composition and comparative 
axial ratios of the four commoner isomorphs are as follows (assuming 
JP(Ti2) as the groundform of clmozoisite) 

Clmozoisite Ca 2 Ala (OH) (8104)3 i 4457 . i i 8057 

Epidote Ca*(Al Fe) 8 (OH)(Si04)s 15807 i i 8057, =64 36' 
Piedmontite Ca 2 (Al Mn)s (OH) (8104)3 i 6100 i i 8326, 0= 64 39' 
Allaxute Ca 2 (Al Ce Fe)s (OH) (8104)3 i SS9 J * 7 6 9*, 18=64 59' 



Clmozoisite is rare, though its molecule occurs abundantly m iso- 
morphous mixtures with the corresponding iron molecule m epidote 

Zoisite (Ca 2 Als(OH)(Si04)3) 

Zoisite is a calcium, aluminium orthosilicate containing only a small 
quantity of the corresponding iron molecule The theoretical composi- 
tion of the pure Ca molecule is 



810=3952, Al 2 0s=339 2 > CaO=24$9, H 2 0=i97 Total=ioooo 

Colored varieties contain a little iron or manganese Green crystals (I), 
from Ducktown, Tenn , and red crystals (thvtee) (II), from Kleppan, m 
Norway, analyze as follows 

Si0 2 A1 2 3 Fe 2 3 FeO CaO MgO Mn 2 3 Na 2 H 2 Total 

I 39 61 32 89 91 71 24 So 14 2 12 100 88 

II 42,81 31 14 2 29 18 73 i 63 i 89 64 99 13 

Zoisite crystallizes m the orthorhombic system (orthorhombic bi- 
pyramidal class), with the axial ratio 6196 : i 3429. Its crystals are 



ANHYDROUS ORTHOSILICATES 



327 




usually simple and without end faces The most frequent forms are 
ooP(no), ooP4(i 4 o), oo P 06(010) P(in),2Pco(o2i)and4Po6(o4i) 
are the commonest terminations (Fig 178) The crystals are all pris- 
matic and are striated longitudinally Their 
cleavage is perfect parallel to oo P 86 (oio) 
The angle no A 110=63 34'. 

The mineral is ash-gray, yellowish gray, 
greenish white, green or red in color and has a 
white streak The rose-red variety, contain- 
ing manganese, is known as thuhte Very 
pure fresh zoisite is transparent, but the ordi- 
nary forms of the mineral are translucent 
Its luster is glassy, except on the cleavage 
surface, where it is sometimes pearly Its 
fracture is uneven Its hardness is 6 and 
density about 33 In specimens from Duck- 
town, Tenn , a=i 7002, /3=i 7025, 7=1 7058 
for yellow light A notable fact in connection FIG 178 Zoisite Crystal 
with this mineral is that with increase of the with*)?, no(), ooPx, 

molecule Ca 2 Fe3(OH)(Si0 4 )3 in the mixture OIO J 6) p 4' ^ > 

sPoo, 021 (it) and P, in 

' 



.* 



the plane of its optical axes tends to change 
from oP(oio) to oo P 06 (ooi) 

Zoisite fuses to a clear glass before the blowpipe and gives off water, 
which causes a bubbling on the edges of the heated fragments It is 
only slightly affected by acids, but after heating it is decomposed by 
hydrochloric acid with the production of gelatinous silica 

Occurrence The mineral occurs as a constituent of crystalline 
schists, especially those rich in hornblende, or of quartz veins traversing 
them It is also a component of the alteration product known as 
saussitnte which results from the decomposition of the plagioclase 
(p. 418) m certain basic, augitic rocks known as gabbros It is thus a 
product of metamorphism 

Localities Good crystals of zoisite are found near Pregratten in 
Tyrol, at Kleppan (thuhte), Parish Souland, Norway, and in the ore 
veins at the copper mines of Ducktown, Tenn , where it is associated with 
chalcopyrite, pynte and quartz. 

Epidote (Ca 2 (Al-Fe) 3 (OH)(Si0 4 )3) 

Epidote, or pistazite, differs from the monochnic dimorph of zoisite 
(dmozoisite) in containing an admixture of the corresponding iron sfli- 
cate which is unknown as an independent mineral. 



328 DESCRIPTIVE MINERALOGY 

Since it consists of a mixture of an aluminium and an iron compound 
its composition necessarily vanes The four lines of figures below give 
the calculated composition of mixtures containing 15 per cent, 21 per 
cent, 30 per cent and 40 per cent of the iron molecule 

Per cent 



Si0 2 


A1 2 3 


Fe 2 3 


CaO 


H 2 O 


Total 


38 60 


28 80 


6 65 


24 02 


i 93 


100 00 


38 23 


26 76 


9 32 


23 78 


i 91 


100 00 


37 67 


23 71 


13 3i 


23 43 


i 88 


100 00 


37 04 


20 32 


17 75 


23 04 


* 85 


100 00 



21 

30 
40 

Most specimens contain small quantities of Mg, Fe, Mn, Na or K 

Epidote is isomorphous with chnozoisite, crystallizing in the mono- 



\ 




FIG 179 Epidote Crystals with o P 55 , 100 (a), oP, 001(0), P w , 10! (r), |P 55 , 
102 (), PI nI () and P ob , on (0) 




*FiG 180 Epidote Crystals with a, c, r, *, wand as m Fig 179 Also oop, 
iio(w), 2PS6, 2oT(0, -P 55 , ioi W, -3?!, W (/O and JP5, 423 (/) 

clime system (monochmc prismatic class), with the axial ratio i 5787 i 
: 18036. #=64 36'. The mineral is remarkable for its handsome 
crystals, many of which are extremely rich in forms The crystals are 
usually columnar in consequence of their elongation parallel to the b 
axis The most prominent forms are oo P 56 (100), oP(ooi), ^P 56 (20!) 
P w (jol), P(nl), oo P(no) and P 5b (on) (Fig, 179 and 180) In addi- 
tion to these, over 300 other forms have been identified Twinning 
is common, with oop^(ioo) the twinning plane The angle no A 
ilo= 109 56'. 

Epidote is yellowish green, pistachio green, dark green, brown or, 
rarely, red It is transparent or translucent and strongly pleochroic. 
In green varieties the ray vibrating parallel to the b axis is brown, that 
vibrating nearly parallel to c, yellow, and that vibrating perpendicular to 



ANHYDROUS ORTHOSILICATES 329 

the plane of these two is green Its luster is glassy and its streak gray 
Its cleavage is very perfect parallel to oP(ooi) Its hardness is 6 5 and 
density 3 3 to 3 5 The refractive indices for yellow light m a crystal 
from Zillerthal are 05=17238, /5=i 7291, 7=1 7343 They increase 
with the proportion of the iron molecule present, being i 7336, i 7593 
and i 7710 :n a specimen containing 27 per cent of the iron epidote 

The varieties that have been given distinct names are. 

BucUwidite, a greenish black variety in crystals that are not elon- 
gated, 

Wtthanwte, a bright red variety containing a little MnO. 

Fragments of the mineral when heated before the blowpipe yield 
water and fuse to a dark brown or black mass that is often magnetic 
With increase in iron fusion becomes more easy. Before fusion epidote 
is practically insoluble in acid. After heating HC1 decomposes it with 
the separation of gelatinous silica 

The ordinary forms of the mineral are characterized by their yellow- 
ish green color, ready fusibility and crystallization 

Occurrence and Origin Epidote occurs in massive veins cutting crys- 
talline schists and igneous rocks, as isolated crystals and druses on the 
walls of fissures through almost any rock and in any cavities that may 
be in them, and as the pnncipal constituent of the rock known as epi- 
dosite It is a common alteration product of the feldspars (p. 408), 
pyroxenes (p 364), garnet, and other calcium and iron-bearing minerals 
Pseudomorphs of epidote after these minerals are well known. The 
mineral is a weathering product, but is more commonly a product of 
contact and regional metamorphism. 

It has not been produced artificially 

Localities Epidote crystals are so widely spread that only a few of 
the important localities in which they have been found can be mentioned 
here. Particularly fine crystals occur m the Sulzbachtibal, Salzburg, 
Austria, in the Zillerthal, in Tyrol, near Zermatt, in Switzerland, in 
the Alathal, Traversella, Italy, at Arendal, Norway, in Japan, at 
Prince of Wales Island, Alaska, and at many other points in North 
America 

Piedmontite (Ca2(Al-Mn) 3 (OH)(SiO 4 ) 3 ) 

Piedmontite is the manganese epidote, differing from the ordinary 
epidote in possessing manganese in place of iron Usually, however, 
the iron and the manganese molecules are both present. Typical analy- 
ses of crystals from St. Marcel, in Piedmont, Italy (I), Otakisan, Japan 
(II), and Pine Mt , near Monterey, Md (III), follow 



330 DESCRIPTIVE MINERALOGY 

Si0 2 A1 2 3 Mn 2 3 MnO Fe 2 3 MgO CaO H 2 Total 

I 35 68 18 93 14 27 3 22 i 34 24 32 2 24 100 oo 

II 36 16 22 52 6 43* 9 33 40 22 05 3 20 100 53* 

III 47 37 18 ss 6 85 i 92 4 02 25 15 82 2 08 100 05* 

* II contains also 44 per cent Na2<D The M^Oa contained also MnO 



III contains also 2 03 per cent of the oxides of rare earths, 14 per cent PbO, 
ii per cent CuO, 23 per cent Na.O and 68 per cent K^O The specimen contained 
also a little admixed quartz which was determined with the SiOj 

The axial ratio of piedmontite is i 6100 i . i 8326 18=64 39' 
Its crystals are similar m habit to those of epidote, but they are much 
simpler The most prominent forms are oo P 60 (100), oP(ooi), P(In), 
P66(To2), ooP5b(oio) and ooP(no) Twins are fairly common, 
with oo P 56 (too) the twinning plane. 

The mineral is rose-red, brownish red or reddish black It is trans- 
parent or translucent and strongly pleochroic in yellow and red tints 
and has a glassy luster and pink streak It is brittle, and has a good 
cleavage parallel to oP(ooi) Its hardness is 6 and density 3 40. Its 
refractive indices are the same as those of epidote. 

Before the blowpipe piedmontite melts to a blebby black glass and 
gives the manganese reaction in the borax bead. It is unattacked by 
acids until after heating, when it decomposes m HC1 with the separation 
of gelatinous silica 

It is characterized by its color and hardness and by its manganese 
reaction 

Occurrence and Origin Piedmontite occurs as an essential constit- 
uent of certain schistose rocks that are known as piedmontite schists 
It occurs also m veins and m certain volcanic locks, where it is probably 
an alteration product of feldspar. Its methods of origin are the same 
as those of epidote 

Localities Good crystals are found in the manganese ore veins at 
St. Marcel, Piedmont, on ilmenite in crystalline schists on the Isle of 
Groix, off the south coast of Brittany, and at a number of points on the 
Island of Shikoku, Japan, in crystalline schists and in ore veins In 
the United States it is so abundant m the acid volcanic rocks of South 
Mountain, Penn., as to give them a rose-red color. 

Allanite (Ca 2 (Al-Ce-Fe)3(OH)(SiO 4 )3) 

Allanite is a comparatively rare epidote m which there are present 
notable quantities of Ce, Y, La, Di, Er and occasionally other of the 
rarer elements Since cerium is present in the largest quantity the 



ANHYDROUS ORTHOSILICATES 331 

formula of the mineral is usually written as above, with the under- 
standing that a portion of the cenum may be replaced by yttrium and 
the other elements Some idea of the complex character of" the numeral 
may be gained from the two analyses quoted below The first is of 
crystals from Miask, Ural, and the second of a black massive variety 
from Douglas Co , Colo 

I II 

Si0 2 30 81 31 13 

Al 2 0s 16 25 ii 44 

Fe 2 O 3 6 29 6 24 

Ce 2 O 3 10 13 12 50 

BeO 27 

Di 2 3 3 43 

La 2 3 635 
Y 2 3 i 24 

FeO 8 14 13 59 

MnO 2 25 61 

MgO 13 16 

CaO 10 43 9 44 

K20 53 tr 

Na 2 56 

H 2 2 79 2 78 

C0 2 21 



Total 98 77 99 8r 

Allarute rarely occurs in crystals, but when these are found they are 
usually more complex than those of piedmontite but much less compli- 
cated than those of epidote. Their axial ratio is i 5509 : i : 1 7691 
with =64 59' Their habit is like that of epidote crystals Common 
forms are ooFco(ioo), oP(ooi), P(iio) Twins are like those of 
epidote The mineral usually occurs as massive, granular or columnar 
aggregates, or as ill-defined columnar crystals resembling rusty nails 
It sometimes forms parallel mtergrowths with epidote. 

It is black on a fresh fracture and rusty brown on exposed surfaces, 
and has a greenish gray or brown streak It has a glassy luster and is 
translucent in thin splinters, with greenish gray or brownish tints and 
is pleochroic in various shades of brown Its hardness is 5-6 and 
density 3-4, both varying with freshness and composition The cleav- 
ages are imperfect and the fracture uneven Its indices of refraction 
are nearly the same as those of epidote. 



332 DESCRIPTIVE MINERALOGY 

Small fragments of fresh allanite fuse to a blebby black magnetic 
glass before the blowpipe and are decomposed by HC1 with the separa- 
tion of gelatinous silica 

Allamte is distinguished by its color, manner of occurrence, and the 
reaction for water in the closed tube 

The mineral alters readily on exposure to the weather, yielding 
among other compounds mica and hmonite 

Occurrence Allanite occurs as an original constituent in some 
granites, and other coarse-grained rocks It is found also in gneisses, 
occasionally in volcanic rocks and rarely as a metamorphic mineral in 
crystalline limestones 

Localities The best crystals have been found m the druses of a 
volcanic rock at Lake Laach, Prussia, in coarse-grained granitic rocks 
at several places in the Tyrol, in the limestone at Pargas, Finland, and 
at various points in Ural, Russia Massive allanite occurs in the coarse 
granite veins at Hittero, Norway and as the constituents of granites 
at many places in the United States Parallel mtergrowths with epidote 
are found in granite at Ilchester, Md 

CHONDRODITE GROUP 

The chondrodite group of minerals includes four members of the 
general formula (Mg(F OH^Mg^SiO^y in which x equals i, 3, 5, 7, and 
y, i, 2, 3, 4 Of these, one (humite) may be orthorhombic The other 
three are monochmc with the angle =90 The four members of the 
group with their compositions and axial ratios are 







Prolectite (Mg(F OH) 2 )Mg(Si0 4 ) i 0803 i i 8862 18=90' 
Chondrodite (Mg(F OH) 2 )Mg 3 (SiO 4 ) 2 i 0863 i 3 1445 =90 

b Z 

Humite (Mg(F OH) 2 )Mg 5 (Si0 4 ) 3 i 0802 '1.4 4033 
Clinohumtte (Mg(F OH) 2 )Mg 7 (Si0 4 ) 4 r 0803 i 5 6588 =90 

To show the similarity in the ratios between the lateral axes of the 
four minerals, the & axis of humite is written as i Chondrodite, humite 
and clmohumite frequently occur together Chondrodite has been 
reported at more localities than either humite or clmohumite, but it is 
not certain that much of it is not chnohumite The three minerals 
resemble one another very closely They are relatively unstable under 
conditions prevailing at moderate depths in the earth's crust, passing 
easily into serpentine, brucite or dolomite Only chondrodite is de- 
scribed. 



ANHYDROUS ORTHOSILICATES 



333 



Chondrodite (Mg3(Mg(F-OHJ 2 )(Si0 4 )2) 

Chondrodite is a rather uncommon mineral that occurs mainly as a 
constituent of metamorphosed limestones that have been penetrated 
by gases and water emanating from igneous rocks It is a characteris- 
tic contact mineral 

Its composition varies somewhat m consequence of the fact that OH 
and F possess the power to mutually replace one another The two 
analyses below are typical of varieties containing a maximum amount 
of F 

Si02 MgO FeO H 2 F F=0 Total 

I 33 77 57 9 8 3 9 6 * 37 5 14=102 222 16 100 06 
II 35 42 54 22 5 72 9 00=104 36-3 78 100 58 

I. Crystals from, limestone inclusions in the lava of Vesuvius 
II. Grains separated from the limestone of the Tilly Foster Iron Mine, Brewster, 
N Y 

Chondrodite is monoclmic (prismatic class), with an axial ratio 
i 0863 11:3 1445 18=90 The crystals vary widely in habit and 
are often complex The forms oP(ooi), 
oo P 66 (100), oo P oo (oio) and various unit 
and clmohemipyramids of the general sym- 
bol x?2 are frequently present, but other 
forms are also common (Fig 181) Twin- 
ning about oP(ooi) is also common 
Usually, however, the mineral occurs m 
little rounded grains, in some instances 
showing crystal faces, scattered through FIG 181 Chondrodite Crys- 
hmestone tel ^ P : & *** 

When fresh, Chondrodite has a glassy 1" v 2 ' " 7 z' * 2 ' 
luster, is translucent and is white or has a _ 2 p* 2 , 121 (r 4 )', p, ni 
light or dark yellow, brown or garnet color (j^), p, in (- 2 ); 
It has a distinct cleavage parallel to oP(ooi), 
a conchoidal fracture, a hardness of 6 and 
a density of 3 15 Its refractive indices 
for yellow light are: 01=1607, =1619, 
T= i 639 

Before the blowpipe Chondrodite bleaches 

without fusing With acids it decomposes with the production of 
gelatinous silica 




103 to)> jP7 ioi ( &) 

and P^, ioi (e%) The 
a axis runs from right to left 
and the upper left hand 
octant is assumed to be 
minus 



334 DESCRIPTIVE MINERALOGY 

It weathers readily to serpentine, chlorite and brucite, and conse- 
quently many grams are colored dark green or black 

Occurrence Chondrodite, as has been stated, occurs in meta- 
morphosed limestones It also occurs in sulphide ore bodies and m a 
few instances in magnetite deposits It is probably in all cases a pneu- 
matolytic or metamorphic product 

Localities It is found as crystals in the blocks enclosed m the lavas 
of Vesuvius, in the copper mines of Kapveltorp, Sweden, in limestone 
in the Parish of Pargas, Finland, and at the Tilly Foster Iron Mine, at 
Brewster, N Y It occurs as grams in the crystalline limestone of 
Sussex Co , N J , and Orange Co , N Y. 

DATOLTTE GROUP 

The members of the datolite group are four in number, but 
of these only two, viz, datohte (Ca(B OH)Si04) and gadohnite 
(Be2Fe(YO)2(Si04)2J are of sufficient importance to be described here 
Both minerals crystallize similarly in the monoclmic system ('mono- 
clinic prismatic class), with axial ratios that are nearly alike 

Datolite a ' b c 6345 i i 2657 ^ = 89 51' 
Gadohmte a b r= 6273 i 13215 ^ = 89 



Datohte (Ca(B OH)SiO 4 ) 

Datolite, or dathohte, is characteristically a vein mineral 

The composition corresponding to the 
formula given above is 

= 218$; CaO=3Soo, 
Total =100 oo 

Some specimens contain a little AbO,* and 
Fe20a but, m general, crystals that have 
been analyzed give results that are m 
close accord with the theoretical com- 

FIG 182 Datohte Crystal wrth P ositlon ' 

oo POO, zoo (a), OOP, no (m), The mineral crystallizes in fine crys- 
-Poo, 101, (<), iPoo, 102 tals that are often very complicated (Fig 
(*); -P, in (), -P3, 212 ^2) About 115 different forms have 
W, Poo, on (m v ) and JPoo, been observed on ^^ Because of the 

012 (g) 

suppression of some faces by irregular 

growth many of the crystals are columnar in habit, others are tabular. 
Most crystals, however, are nearly equi-dimensional The angle 




ANHYDROUS ORTHOSILlCATES 335 

no /\ 1 10 -64 40' The mineral occurs also in globular, radiating, 
granular and massi\ e forms 

Datohte is colorless or white, when pure, and transparent Often, 
however, it is greenish, yellow, reddish or violet, and translucent. Its 
streak is white and its luster glassy It has no distinct cleavage Its 
fracture is conchoidal Its hardness is 5 and its sp gr about 3. Some 
crystals are pyroelectnc For yellow light, a- 16246, 0=1.6527, 
7=1 6694 

Before the blowpipe it swells, and finally melts to a clear glass and, 
at the same time, it colors the flame green Its powder before heating 
reacts strongly alkaline. After heating this reaction is weaker. The 
mineral loses water when strongly heated, and yields gelatinous silica 
when treated with hydrochloric acid. 

The mineral is characterized by its crystallization, its easy fusibility 
and the flame reaction for boron 

Synthesis Datohte has not been produced artificially. 

Occurrence, Origin and Localities It occurs on the walls of clefts 
in igneous rocks, in pegmatite veins and associated with metallic com- 
pounds in ore veins. It is found in many ore deposits of pneumatolytic 
ongin, notably at Andreasberg in the Harz Mts , at Markirch, in 
Alsace, in the Seisser Alps, in Tyrol, in the Serra dei Zanchetti in the 
Bolognese Apennines, at Arendal, Norway, and at many other places 
In North Amenca it occurs at Deerfield, Mass , at Tariffville, Conn , 
at Bergen Hill, N J , and at several points in the copper districts of 
the Lake Superior region 

Gadolinite (Be 2 Fe(YO) 2 (Si0 4 )2) 

Gadolmite is a rather rare mineral with a composition that is not 
well established Its occurrence is limited to coarse granite veins or 
dikes pegmatites of which it is sometimes a constituent. 

Its theoretical composition is as follows, on the assumption that it is 
analogous to that of datolite 

810=2556, Y 2 3 =4844, FeO=iS32; BeO=io68 Total=ioooo, 
but nearly all specimens contain cermm oxides. Others contain nota- 
ble quantities of erbium or lanthanum oxides and small quantities of 
thorium oxide Nearly all show the presence of Fe20s, AfeOs, CaO and 
MgO, and m some helium has been found 

The mineral is found massive and in rough crystals with an axial 
ratio a : b : c*= 6273 : i : i 3215 0=89 26^'. The crystals show 
comparatively few forms, of which ooP(no), oP(ooi), P>(on), 



336 DESCRIPTIVE MINERALOGY 

JPob(oi2), P(Tn) and P(in) are the most common The> are 
usually columnar in habit and are lough and coarse The angle 
iioA 110=64 12' 

Gadolmite is usually black or greenish black and opaque or trans- 
lucent, but very thm splinters of fresh specimens are translucent or 
transparent in green tints Its luster is glassy or resinous, streak 
greenish gray and fracture conchoidal Its hardness is 6-7 and its 
density about 4-4 5 Upon heating the density increases Many crys- 
tals appear to be made up of isotropic and amsotropic substance, and 
some to consist entirely of isotropic matter This phenomenon has 
been explained in a number of different ways, but no one is entirely satis- 
factory. In general, the isotropic material is believed to be an amor- 
phous alteration form of the amsotropic variety It may be changed 
into the amsotropic form by heating 

The crystallized gadolmite swells up m the blowpipe flame without 
becoming fused and retains its transparency The amorphous variety 
also swells without melting, but yields a grayish green translucent mass 
The mineral phosphoresces when heated to a temperature between that 
of melting zinc and silver. After phosphorescing it is unattacked by 
hydrochloric acid Before heating it gelatinizes with the same reagent 
The mineral is weakly radioactive 

Localities and, Origin Gadolmite occurs in the pegmatites of Ytterby 
near Stockholm, and of Fahlun, Sweden, on the Island of Hittero, in 
southern Norway, in the Radauthal, in Harz, at Barringer Hill, Llano 
Co , Texas, as nodular masses and large rough crystals, and at Devil's 
Head, Douglas Co, Colo In the last locality it occurs in a de- 
composed granite as a black isotropic variety with a very complex 
composition Specimens analyzed as follows 

I H 

Si02 22 13 21 86 

Th0 2 89 81 

AbOs 2 34 54 

Fe20a i 13 3 S9 



ii 10 6 87 

(La Di)20a 21 23 19 10 

Y 2 0g . 9 50 12 63 

ErgOs . , ,. 12.74 15 80 



I 



FeO 10 43 

BeO 7 19 

CaO 34 

H 2 . 86 

Other 60 



Total , , 100 48 100 02 



It has apparently in some cases solidified from an igneous magma. 
In others it is of pneumatolytic origin 



ANHYDROUS ORTHOSILICATES 



337 



StauroUte (Fe(AlOH)(A10) 4 (Si0 4 ) 2 ) 

Staurolite is a mineral that is interesting from the fact that it fre- 
quently forms twinned crystals that resemble a cross in shape, and which 
consequently, during the Middle Ages, was held in great veneration 
Its composition is not well established The composition indicated by 
the formula above is as shown in the first line below (I) Three analyses 
are quoted in the next three lines 



A1 2 3 


Fe 2 3 


FeO 


MgO 


H 2 


55 9 




158 




2 00 


54 20 


6 83 


Q 13 




i 43 


51 16 




14 66 


2 73 


i 26 


52 92 


6 87 


7 80 


3 28 


1 59 



Total 
100 oo 
98 97 
loo 33 
100 37 



SiOo A1 2 3 Fe 2 3 FeO MgO H 2 Ti0 2 

I 26 3 

II 27 38 

HI 30 23 

IV 27 91 

I Theoretical composition 

II From Monte Campione, Switzerland 

III From Morbihan, France 

IV From Chesterfield, Mass 

Staurolite crystallizes in the orthorhombic system (bipyramidal 
class) in simple crystals with the axial ratio 4734 * i : 6828 The indi- 





FIG 183 FIG 184 FIG 185 

FIG 183 Staurolite Crystal with ooP, no (ni), oopoo, 100 (&), oP, ooi (c) and 

P 60,101 (r) 

FIG 184 Staurohte Crystal Twinned about |P oo (032) 
FIG 185 Staurolite Crystal Twinned about |P} (232) 

vidual crystals are usually bounded by oo P(no), oo P 65 (ooi), P 55 (101) 
and often oP(ooi), but all their faces are rough (Fig 183) The angle 
1 10 A i io =50 40' More common, however, than the simple crystals 
are interpenetration twins The most common of these are of two kinds, 
(i) with f P 06 (032) the twinning plane (Fig 184), and (2) with |P|(232) 
the twinning plane (Fig. 185) Both types of twins yield crosses, but 
the arms of the first type are perpendicular to one another and those of 



338 DESCRIPTIVE MINERALOGY 

the second type make angles of about 60 and 120 Sometimes the 
twinning is repeated, giving rise to trillings 

The mineral is reddish or blackish brown, and has a glassy or greasy 
luster. Its streak is white It is slightly translucent in fresh crystals, 
but usually is opaque In very thin pieces it is pleochroic in hyacinth- 
red and golden yellow tints Its cleavage is distinct parallel to oo P 06 
(oio) and indistinct parallel to ooP(no) Its fracture is conchoidal, 
its hardness 7 and its density 34~3 8 For yellow light, QJ=I 736, 
/3=i 741, 7= i 746 

Before the blowpipe staurohte is infusible, unless it contains man- 
ganese, in which case it fuses to a black magnetic glass It is only 
slightly attacked by sulphuric acid 

It is distinguished from other minerals by its crystallization, m- 
fusibility and hardness 

Staurolite weathers fairly readily into micaceous minerals, such as 
chlorite (p 428) and muscovite (p. 355) 

Synthesis It has not been produced in the laboratory 

Occurrence The mineral occurs principal!} m mica schist and other 
schistose rocks where it is the result of regional or contact metamor- 
phism Because of its method of occurrence it frequently contains 
numerous mineral inclusions, among them garnet and mica 

Localities Good crystals of staurohte are found in the schists at 
Mte Campione, Switzerland, in the Zillerthal, Tyrol, at Aschaff en- 
burg, in Bavana, at various places in Brittany, France, and in the 
United States, at Wmdham, Maine, at Francoma, N H , at Chester- 
field, Mass , in Patrick Co , Va , and m Fannm Co , N C 

Uses Twins of staurohte are used, to a slight extent, as jewelry. 
Specimens from Patrick Co , Virginia, are mounted and worn as charms 
under the name of " Fairy Stones." 

Dumortierite (Al(AlO) 7 H(BO)(SiOi)3) 

Dumortierite is one of the few blue silicates known It is a borosili- 
cate with a composition approaching the formula indicated above The 
analysis of a sample from Clip, Arizona, gave (I) 



SiO 2 AbOs Fe 2 3 Ti^Oa MgO B 2 3 P 2 0r> Lossonlgn Total 

I. 27 99 64 49 tr 4 95 20 i 72 99 35 

II. 28 58 63 31 21 i 49 5 2i r 53 ioo 33 

Specimens from California (II) contain in addition notable quantities 
of TiCfe, which is thought to exist as Ti 2 03 replacing a part of the AkOa. 



ANHYDROUS ORTHOSILICATES 339 

The mineral crystallizes in the orthorhombic s>stem in aggregates of 
fibers, needles or very thin prisms exhibiting only ooP(no) and 
oo P oo (100) without end faces Its axial ratio is a . b= 5317 : i, and 
the prismatic angle no A 110=56 Its crystals possess a distinct 
cleavage parallel to oo P 66 (100) and a fracture perpendicular to the 
long axes of the prisms Twinning is common, ^ith ooP(no) the 
twinning plane 

Dumortierite is commonly some shade of blue, but in some cases is 
green, lavender, white, or colorless It is translucent or transparent 
and strongly pleochroic, being colorless and red, purple or blue Its 
streak is light blue Hardness is 7 and density 3 3 Its refractive indices 
for yellow light are a= r 678, /3= i 686, 7= i 089 

Before the blowpipe the mineral loses its color and is infusible. It is 
insoluble m acids 

It is distinguished from other blue silicates by its fibrous or columnar 
character and its insolubility m acids 

Its principal alteration products are kaolin and damourite 
(pp 404, 357) 

Occurrence and Locates Dumortierite occurs only as a constit- 
uent of gneisses and pegmatites It is found in pegmatite near Lyons, 
France, near Schmiedeberg, m Silesia, at Harlem, N Y, in a granular 
quartz, at Clip, Yuma Co , Ariz , and in a dike rock composed of quartz 
and dumortiente, near Dehesa, San Diego Co , Cal It is evidently 
a pneumatolytic mineral Its common associates are kyamte, anda- 
lusite or sillimanite 

SODALITE GROUP 

The sodahte group includes a series of isometric minerals that may be 
regarded as compounds of silicates with a sulphate, a sulphide or a chlor- 
ide, or, perhaps better, as silicates in which are present radicals con- 
taining Cl, SO4 and S The minerals comprising the group are hauymte, 
nosean, sodalite and lasnnte* Of these, sodahte appears to be a mixture 
of 3NaAlSiO4 and NaCl, in which the Cl has combined with one atom of 
Al, thus Na4(ClAl)Al 2 (SiC>4)3 The other members of the group are 
comparable with this on the assumption that the Cl atom is replaced by 
the radicals NaS04, and NaSa It is possible, however, that all are 
molecular compounds as indicated by the second set of formulas given 
below. All are essentially sodium salts, except that in typical haiiynite 
a portion of the Na is replaced by Ca. The chemical symbols of the 
four minerals with the calculated percentages of silica, alumina and 
soda corresponding to their formulas are: 



340 



DESCRIPTIVE MINERALOGY 



Si0 2 A1 2 3 Na 2 
37 14 31 60 25 60 



31 65 27 03 27 26 



Sodalite Na4(Cl Al) Al 2 (Si0 4 )3, or 

3NaAlSi04 NaCl 
Noselite Na4(NaSQi Al)Al 2 (Si0 4 ) 3 , 01 

3 NaAlSi0 4 Na 2 S04 
Hauymte (Na 2 Ca)2(NaSOrAl)Ab(SiO 1 ) 3 , or 3199 2732 16.53 

3 NaAlSi0 4 CaSO 4 

Lasurxte Na 4 (NaS 3 Al) A1 2 (8104)3, or 31,7 26,9 27.3 

Na 2 S S* 



Sodalite 



A1)A1 2 (8104)3) 



Sodalite, theoretically, is the pure sodium compound corresponding 
to the composition indicated by the formula given above Natural 
crystals, however, usually contain a little potassium in place of some of 
the sodium and often some calcium, as indicated by the analyses of 
material from Montreal, Canada (I), and Litchfield, Maine (II), quoted 
below Moreover, their content of Cl is not constant 

Si0 2 A1 2 3 Na 2 K 2 OCaO Cl C1O Total 

I 3752 3*38 2515 78 35 691 - 10209 -155 10054 

II 3733 3187 2456 10 . 683 = 10176* -154 10022 

* Includes I 07 per cent H 2 

Sodalite occurs massive and in crystals that appear to be holohedral, 
but etch figures indicate that they are probably tetrahedrally hemi- 
hedral (hextetrahedral class) Most crystals 
are dodecahedral m habit, though some are 
tetrahexahedral and others octahedral The 
forms usually developed are ooO(no), 
ooQoo (100), 0(iu), 202(112) and 404(114). 
Interpenetration twins of two dodecahedrons 
are common, with the twinning plane (Fig 
186) These often possess an hexagonal habit, 
The mineral is colorless, white or some 
light shade of blue or red, and its streak is 
white Its luster is vitreous It is trans- 
parent, translucent and sometimes opaque 
Its cleavage is perfect parallel to ooO(no) 

and its fracture conchoidal Its hardness is 5-5,6, and its density 
2 3. Its refractive index for yellow light, n= 14827 Some specimens 
are distinctly fluorescent and phosphorescent. 




FIG 186 Sodalite Inter- 
penetration Twin of Two 
Dodecahedrons Elon- 
gated in the Direction of 
an Octahedral Axis and 
Twinned about 0(m) 



ANHYDROUS ORTHOSILICATES 341 

Before the blowpipe, colored varieties bleach and all varieties swell 
and fuse readily to a colorless blebby glass The mineral dissolves com- 
pletely in strong acids and yields gelatinous silica, especially after heat- 
ing When dissolved in dilute nitric acid its solution yields a chlorine 
precipitate with siher nitrate Its powder becomes bro\\n on treatment 
with AgNOs, in consequence of the production of AgCl 

The mineral is best distinguished from other similarly appearing 
minerals by the production of gelatinous silica with acids and the reac- 
tion for chlorine 

As a result of weathering sodahte loses Cl and Na and gams water 
Its commonest alteration products are zeolites (p 445), kaolin (p 440), 
and muscovite (p 355) 

Syntheses It has been produced artificially by dissolving nepheline 
ponder in fused sodium chloride, and by decomposing muscovite 
with sodium hydroxide and NaCl at a temperature of 500 C 

Occurrence and Ortgm Sodahte occurs principally as a constituent 
of igneous rocks rich in alkalies and as crystals on the walls of pores in 
some lavas It is also known as an alteration product of nephehne 

Localities Good crystals are found in nepheline syenite at Ditro, 
in Hungary, in the lavas of Mte Somma, Italy, in the pegmatites of 
southern Norway; and at many other points where nephehne rocks 
occur In North America it is abundant in the rocks at Brome, near 
Montreal, in the Crazy Mts , Montana, and at Litchfield, Maine The 
material at the last-named locality is light blue 

Noselite and Haiiymte ((Na^CaHNaSCX Al)Al 2 (Si0 4 ) 3 ) 

Noselite, or nosean, and hauynite, or hauyn, consist of isomorphous 
mixtures of sodium and calcium molecules of the general formula given 
above Those mixtures containing a small quantity of calcium are 
usually called nosean, while those with larger amounts constitute hauyn. 
The theoretical nosean and hauyn molecules are indicated on p 340 
The theoretical compositions of the pure nosean molecule (I) and of the 
most common hauyn mixture (II) are as follows 

SiO 2 A1 2 3 Fe 2 3 CaO Na 2 Ka 2 S0 3 H 2 Total 

I 31 65 27 03 27 26 14 06 100 oo 

II 31 99 27 32 9 94 16 53 14 22 100 oo 

HI 35 99 29 41 31 21 20 91 10 58 i 63 99 61 

IV 33 78 27 42 10 08 13 26 3 23 12 31 . 100 08 

* Contains also 57 per cent Cl 



342 DESCRIPTIVE MINERALOGY 

In line III is the analysis of a blue nosean from Siderao, Cape Verde, 
and in line IV, the analysis of a blue haiiyn from the lava of Monte Vul- 
ture, near Melfi, Italy 

Nosean and hauyn are isomorphous with sodalite They crystallize 
is the isometric system in simple combinations with a dodecahedral 
habit The principal forms observed aie ooO(no), ooOoo(ioo) 
0002(102), 0(in) and 202(112) Contact and mterpcnetration twins 
are common, with 0(m) the twinning plane The twins are often 
columnar. 

The minerals have a glassy or greasy luster, are transparent or trans- 
lucent, have a distinct cleavage parallel to ooQ(iio) and an uneven or 
conchoidal fracture Their hardness is 5 6 and density 2 25 to 2 5, the 
value increasing with the amount of CaO present Nosean is generally 
gray and hauyn blue, but both minerals may possess almost any color, 
from -white through light green and blue tints to black Red colors are 
rare The streaks of both minerals are colorless, or bluish For yel- 
low, light #=14890 to i 5038, increasing with increase m the Ca 
present Both minerals are fluorescent and phosphorescent. 

Before the blowpipe both minerals fuse with difficulty to a blebby 
white glass, the blue hauyn retaining its color until a high temperature 
is reached In this respect it differs from blue sodalite which bleaches 
at comparatively low temperatures Upon treatment with hot water 
both minerals yield NaaS04 They are decomposed with acids yielding 
gelatinous silica The powders of both minerals react alkaline Both 
also give the sulphur reaction with soda on charcoal 

The minerals are easily distinguished from all others by their crys- 
tallization, gelatmization with acids and reaction for sulphur. 

Both minerals upon weathering yield kaolin or zeolites and 
calcite 

Synthesis Crystals of nosehte have been made by melting together 
Na2C03, kaolmite and a large excess of Na2SO* 

Occurrence Hauyn and nosean occur in many rocks containing 
nephehne, especially those of volcanic origin and m a few metamorphic 
rocks. Hauyn is so common m some of them as to constitute an essen- 
tial component 

Localities Both minerals are found in good crystals in metamor- 
phosed inclusions in the volcanic rocks of the Lake Laach region, in 
Prussia, also in the rocks of the Kaiserstuhl, m Baden, in those of 
the Albanian Hills, in Italy, and at S. Antao in Cape Verde In 
America haiiyn has been reported from the nephelme rocks of the 
Crazy Mts,, Montana, 



ANHYDROUS ORTHOSILICATES 343 

Lasunte (Na 4 (NaS 3 - Al)Al 2 (Si0 4 ) 3 ) 

Lasunte is better known as lapis lazuli It is bright blue in color 
and was formerly much used as a gem stone The material utilized for 
gem purposes is usually a mixture of different minerals, but its blue 
color is given it by a substance with a composition corresponding to the 
formula indicated above Since the artificial ultramarine, which is 
ground and used as a pigment, also has this composition, the molecule is 
sometimes represented by the shortened symbol USs, or if it contains 
but two atoms of S, by the symbol US2 The deep blue lasunte from 
Asia contains as its coloring material a substance with a composition 
that may be represented by 15 7 molecules of USs, 76 9 molecules of 
hauyn and 7 4 molecules of sodahte, corresponding to the percentages. 

SiO 2 A1 2 3 CaO Na 2 K 2 

32 52 27 61 6 47 19 45 28 

S0 3 S Cl Total (Less C1 = O) 

10 46 2 71 47 99 97 = 99 42 

Lasunte is thus the name given to the blue coloring matter of lapis 
lazuli, which is a mixture It apparently crystallizes in dodecahedrons 
Its streak is blue, its cleavage is dodecahedral, its hardness about 5 and 
its specific gravity about 2 4 Before the blowpipe it fuses to a white 
glass Its powder bleaches rapidly in hydrochloric acid, decomposes 
with the production of gelatinous silica and yields H 2 S. 

It is distinguished from blue sodalite and hauyn by the reaction with 
HC1, especially by the evolution of H 2 S 

Occurrence Lasunte is principally a contact mineral in limestone. 

Localities Good lapis lazuli occurs at the end of Lake Baikal, in 
Siberia, in the Andes of Ovalle, in Chile, in the limestone inclusions in 
the lavas of Vesuvius, and in the Albanian Mts , Italy 

Uses Lapis lazuli is used as an ornamental stone in the manufacture 
of vases, and various ornaments, in the manufacture of mosaics, and as a 
pigment, when ground, under the name ultramarine Most of tfre ultra- 
marine at present in use, however, is artificially prepared, 

ACID ORTHOSILICATES 
Prehaite (H 2 Ca2Al 2 (SiO 4 ) 3 ) 

Prehmte is nearly always found in crystals, though it occurs also in 
stalactitic and granular masses 

The theoretical composition of the pure mineral is 8102=43.69, 




344 DESCRIPTIVE MINERALOGY 

A1 2 03=>2478, CaO=27i6, and H 2 O = 437 Most crystals, however, 
contain small quantities of FeoOj and other constituents 

SiQ. AUOi I'cjOj KO CaO M0 II.O Total 

Jordansmuhl, Silesia 44" 26 Al 2< > 2 tr 49* 10090 

Cornwall, Penn 4^ 4Q 20 88 5 54 27 o^ ti 4 or 99 85 

Chlorastrohte, Isle Royale 37 41 H 02 2 21 i 81 22 20 3 46 7 72 99 75* 

* Also 32 per cent Na^O 

Its crystallization is orthoihomhic and hcraimoiphic (rhombic py- 
ramidal class), with a b c= 8420 i i 1272 The ciystals vary 
widely in habit, but they contain comparatively few foinis The most 
prominent are oP(ooi), ooP(uo), 6P(o6i), 2P(32i) and 6P(66i) 

(Fig 187) The angle noAiTo=8o 
12' Because they exhibit pyroelectnc 
l>olanty in the direction of the a a.xis the 

crvstals arc thought to be twins, with 
FIG 187 Prehnite Crystal with * _ _ / N . , , . 

OOP/XXO W, OOP/, I0 o Wl P (I*) as the twinning plane 
JP56, 304 (n), JP55, 308 W Cleavage is good parallel to oP(oor) 
and oP, ooi (c) The crystals are frequently tabular 

parallel to oP(ooi), although other 

habits are also common Isolated individuals are rare, usually many 
are grouped together into knotty or warty aggregates 

Prehnite is colorless or light green, and transparent or trans- 
lucent, and it has a colorless streak Its luster is pearly on oP(ooi) but 
glassy on other faces Its fracture is uneven, its hardness 7+ and its 
density 2.80-2 95. For yellow light, a= i 616, 0= i 626, 7 = 1 649 

Before the blowpipe prehnite exfoliates, bleaches and melts to a 
yellowish enamel At a high temperature it yields water Its powder is 
strongly alkaline. It is partially decomposed by strong hydrochloric 
acid with the production of pulverulent silica. After fusion it dissolves 
readily in this acid yielding gelatinous silica 

The mineral has not been produced artificially 

Occurrence Prehnite occurs as crystals implanted on the walls of 
clefts in siliceous rocks, in the gas cavities in lavas, and in the gangue of 
certain ores, especially copper ores It is found also as pseudomorphs 
after analcite (p 438), laumomte (p 451), and xutrohte (p 454) In 
all cases it is probably a secondary product 

Localities Fine crystals come from veins at Harzburg, in Thuringia, 
at Stnegau and Jordansmuhl, Silesia, and at Fassa and other places in 
Tyrol. Good crystals are found also in the Campsie Hills in Scotland. 
The mineral is abundant in veins with copper along the north shore of 



ANHYDROUS ORTHOSILICATES 345 

Lake Superior and on Keweenaw Point, and it occurs also at Farmington, 
Conn , Bergen Hill, N J , and Cornwall, Penn 

Uses The mineral known as chlorastrolite is probably an impure 
prehnite. It is found on the beaches of Isle Royale and the north shore 
of Lake Superior as little pebbles composed of stellar and radial bunches 
of bluish green fibers The pebbles were originally the fillings of gas 
cavities in old lavas The> are polished and used, to a slight extent, as 
gem-stones About $2,000 worth were sold in 1911 and 350 ^orth in 
1912 

Axinite (H(Ca-Fe-Mn) 3 Al 2 B(SiO 4 )4) 

Axmite is especially noteworthy for its richness in crystal forms 
The mineral is a complicated borosihcate for ^vhich the formula given 
above is merely suggestive Analyses of crystals from different localities 
vary so widely that no satisfactory simple formula has been proposed 
for the mineral Four recent analyses are quoted below 

Radauthal Stnegau Oisans Cornwall 

Si02 39 26 42 02 41 53 42 10 



A1 2 O 3 

FeoOs 

FeO 

MnO 

CaO 

MgO 

H 2 O 



4 gi 


OO 


4 62 


4 64 


14 46 


17 73 


17 90 


17 40 


2 62 


93 


3 9 


306 


365 


65S 


4 02 


5 84 


2 80 


6 52 


3 79 


4 63 


29 70 


19 21 


21 66 


20 53 


2 00 


38 


74 


66 


I 22 


i 77 


2 l6 


i 80 



Total 100 62 ico ii 100 32 100 66 

Axinite crystallizes in the trichmc system (pinacoidal class), with 
a : b : c=* 4921 . i : 4797 and 01=82 54', 0=91 5 2 ', 7=i3 l0 3 2 '- 
The crystals are extremely varied m habit but nearly all are somewhat 
tabular parallel to 'P(iTi), oo P'(iio) or oo 'P(iTo) About 45 forms 
have been observed In addition to the three mentioned, 2'?' So (201), 
P'(III), /P(iFi), 2 y P' 06 (021), oo P 06 (oio) and oo P oo (100) are the most 
frequently met with (Figs 188, 189) The plane 'P(iTi) is usually 
striated parallel to its intersection with oo 'P(iTo) The angle 100 A i "10 
= 15 34'. The cleavage is indistinct parallel to ooP'(no) and the 
crystals are strongly pyro electric 

Axinite is brownish, gray, green, bluish or pink, and is strongly pleo- 
chroic in pearl-gray, olive-green and cinnamon-brown tints It is 



346 DESCRIPTIVE MINERALOGY 

transparent or translucent and has a glassy luster and a colorless streak 
Its fracture is conchoidal or uneven It is brittle, has a hardness of 6-7 
and a density of 3 3 For red light, a= i 6720, /3= i 6779, 7 = 1 6810 

Axmite, before the blowpipe, exfoliates and fuses to a dark green 
glass which becomes black in the oxidizing flame It colors the flame 
green, especially upon the addition of KHS04 and CaFo to its powder 
Its powder reacts alkaline It is only slightly attacked by acids. After 





FIG 188 FIG 189 

FIG 188 Aximte Crystal with ooPoo, TOO (a), 2'P'So, 201 (s), ooP/, no (m), 

oo /p ilo (M), P', m (*) and 'P, ill (r) 
FIG 189 Axmite Crystal with M , m, a, r and 5 as m Fig 188 Also ooPoo, 

oio (6), aP' w , 021 (v), yP, In (e), |,P3, 132 (0), 4/P^, 241 (o), 3/P3, 131 (I'), 

00 /'PI. 130 (w), 3'P3, i3i () and 4'?% 241 (<J). 

fusion, however, it dissolves readily with the production of gelatinous 
silica 

The mineral is easily characterized by its crystallization and the 
green color it imparts to the flame 

It has not been produced artificially 

Pseudormorphs of chlorite after axroite have been found in Dart- 
moor, England 

Occurrence Axmite crystals occur in cracks in old siliceous rocks. 
It is found also in ore veins and as a component of a contact rock com- 
posed mainly of augite, hornblende and quartz, occuning near the 
peripheries of granite and diabase masses. It was formed by the aid 
of pneumatolytic processes 

Localities Excellent crystals of axmite are found at Andreasberg 
and other places in the Harz Mts , near Stnegau, m Silesia, near 
Poloma, in Hungary, at the Piz Valatscha, in Switzerland, near Verms 
and at other points m Dauphme, France, at Botallak, Cornwall, Eng- 
land, at Komgsberg, Norway, Nordmark, Sweden; Lake Onega, and 
Miask, Russia, at Wales in Maine and at South Bethlehem, Penn. 




ANHYDROUS ORTHOSILICATES 347 

Dioptase (H2CuSiO4) 

Dioptase is especially interesting because of its crystallization, which 
is rhombohedral tetartohedral (trigonal rhombohedral class) Its crys- 
tals are columnar Their axial ratio is i 5342 They are usually 

bounded by oo P2(ii2o), - 2R(o22i) or R(ioYi) and ~^i - (1341) or 

jT> JL Y 4 ^ 

H - (3141) ( a rhombohedron of the third order, Fig 190) Besides 

occurring as crystals the mineral is found also 
massive and in crystalline aggregates. 

The composition expressed by the formula 
given above is 81023818, CuO=504o; 
H20=n 44, which is approached very closely 
by some analyses. The same composition may 
be expressed by CuSiOs HaO Indeed, recent 
work indicates that the mineral is a hydrated 
metasilicate and not an acid orthosihcate FIG 190 Dioptase Ciys- 

Dioptase has an emerald-green or blackish tai Wlth P2 "20 and 
green color, a glassy luster and a green streak ~~ 2R ' 221 > mtl[L a 
It is transparent or translucent, is brittle 
and its fracture is uneven or conchoidal Its stnations 
hardness is 5 and its density 3 05. It is weakly 

pleochroic and is distinctly pyroelectnc For yellow light, co=i 6580, 
6=17079 

Before tie blowpipe dioptase turns black and colors the flame green. 
On charcoal it turns black in the oxidizing flame and red m the reducing 
flame without fusing It is decomposed by acids with the production of 
gelatinous silica 

Synthesis Crystals of dioptase have been made by allowing mix- 
tures of copper nitrate and potassium silicate to diffuse through a sheet 
of parchment paper 

Occurrence and Localities The mineral occurs in druses on quartz 
in clefts in limestone, and in gold-bearing placers in the Altyn-Tube Mt. 
near the Altyn Ssu River, m Siberia, in crystals on wulfemte and cala- 
mme and embedded in clay near R6zbanya, Hungary, with quartz and 
chrysocolla in the Mmdonli Mine, French Congo, in copper mines at 
Capiapo, Chile, and in Peru, at the Bon Ton Mines, Graham Co , 
Ariz , and near Riverside, Pinal Co,, in the same State. In the Bon 
Ton Mines it covers the walls of cavities in the ore, which consists of a 
mixture of kmomte and copper oxides 



348 



DESCRIPTIVE MINERALOGY 



MICA GROUP 

The mica group comprises a series of silicates that are characterized 
by such perfect cleavages that extremely thin lamellae may be split 
from them with surfaces that are perfectly smooth. The lamellae are 
elastic and in this respect the members of the group are different from 
other minerals that possess an almost equally perfect cleavage Some 
of the micas are of great economic importance, but most of them have 
found little use in the arts 

The micas may be divided into four subgroups, (T) the magnesium- 
iron micas, (2) the calcium micas, (3) the kthium-iron micas, and (4) 
the alkali micas Of the latter there are three subdivisions, (a) the 
lithia micas, () the potash micas, and (c) the soda micas 

All the micas crystallize in the monoclmic system (monoclmic pris- 
matic class), in crystals with an orthorhombic or hexagonal habit 

In composition the micas are complex The alkali micas are ap- 
parently acid orthosihcates of aluminium and an alkali the potash 
mica being KHaAk (8104)3 Other alkali micas are more acid, and 
some of the magnesium-iron micas are very complex The members 
with the best established compositions are apparently salts of orthosilicic 

acid, and, hence, the entire group is placed 
with the orthosihcates 

All the micas possess also, in addition to 
the very noticeable cleavage which yields 
the characteristically thin lamellae that are 
so well known, other planes of parting 
which are well exhibited by the rays of 
the percussion figure (Fig, 191) The 
largest ra} known as the characteristic 
ray is always parallel to the chnopinacoid. 
In some micas the plane of the optical 
axes is the chnopinacoid and m others is 
perpendicular thereto In the latter, known 
as micas of the first order, the plane of 

the axes is perpendicular to the characteristic ray and m the former, 
distinguished as micas of the second order, it is parallel to this ray. 

The value of the optical angle varies widely In the magnesia micas 
it is between o and 15, in the calcium micas between 100 and 120, 
and in the other micas between 55 and 75 When the angle becomes 
zero the mineral is apparently umaxial But etch figures on all micas 
indicate a monoclmic symmetry (compaie Fig 194) 




FIG 191 Percussion Figure 
on Basal Plane of Mica 
The long ray is parallel to 
oo Pob (oio) 



ANPIYDROUS ORTHOSILICATES 



349 



THE MAGNESIUM-IRON MICAS 

Biotite ((K H) 2 (Mg Fe) 2 (Al Fe) 2 (Si0 4 ) 3 ) 

The magnesium-iron micas are usually designated as biotite. 
group includes micas of both orders as follows 



This 



isl Order 
Anomite 



2d Oraer 
Meroocene 
Lepidomelane 
PUogopiU 



The crystals of biotite have an axial ratio 5774 i : 3 2904 with 
$= 90 They are usually simple combinations of oP(ooi), oo P ob (oio), 
|P(ii2) and P(Tn) (Fig 192). Twins are 
common, with the twinning plane perpendic- 
ular to oP(ooi) The composition face may 
be the same as the twinning plane or it may be 
193) 



witu oP, ooi (c), ooPSb, 
oio (6), P, In (ju) and 
-JP 112 (<?) 



oP(ooi) (Fig 193) The crystals have an 

hexagonal habit, the angle IiiAoio being FlG ^ ***~^* ^ystel 

60 22!'. The mineral also occurs in flat 

scales and in scaly aggregates 

The color of biotites varies from yellow, 
through green and brown to black Pleochroism is strong in sections 
perpendicular to the perfect cleavage, ie, perpendicular to oP(ooi) 
The streak of all varieties is white Their hardness =2.5 and density 
27-3.1, depending upon composition. The refractive indices for yellow 




FIG. 193 Biotite Twinned about a Plane Perpendicular to oP (ooi), and Parallel 
to the Edge Between oP(ooi) and aP(22i) The composition plane is 
oP(ooi) Mica law A=nght hand twin, B and C-left hand twins. 

light m a light brown biotite from Vesuvius are' a 1.5412, /3=i 5745. 
They are higher m darker varieties. 

Etch figures are produced by the action of hot concentrated sulphuric 
acid, 

Varieties and their Localities Anomite is rare. It occurs at Green- 
wood Furnace, Orange Co , N Y., and at Lake Baikal, m Siberia 



350 DESCRIPTIVE MINERALOGY 

Meroxene is the name given to the common biotite of the 2d order 
It occurs m particularly fine crystals in the limestone blocks included 
in the lava of Mte Somma, Naples, Italy, at various points in Switzer- 
land, Austria and Hungary, and at many other points abroad and in 
this country 

Lepidomelane is a black meroxene characterized by the presence 
in it of large quantities of ferric iron It is essentially a magnesium-free 
biotite It occurs in igneous rocks, especially those rich in alkalies 
Two of its best known occurrences in the United States are in the nephe- 
hne syenite at Litchfield, Maine, and in a pegmatite in the northern part 
of Baltimore, Md 

Phlogopite, or amber mica, is the nearly pure magnesium biotite 
which by most mineralogists is regarded as a distinct mineral, partly 
because m nearly all cases it contains fluorine Its color is yellowish 
brown, brownish red, brownish yellow, green or white Its luster is 
often pearly, and it frequently exhibits astensm in consequence of the 
presence of inclusions of acicular crystals of rutile or tourmaline arranged 
along the rays of the pressure figure Its axial angle is small, increasing 
with increase of iron Its refractive indices are a=i 562, =i 606, 
7=1 606 

Phlogopite is especially characteristic of metamorphosed limestones 
It occurs abundantly in the metamorphosed limestones around Easton, 
Pa , at Edwards, St Lawrence Co , N Y , and at South Burgess, 
Ontario, Canada. It is also found as a pyrogenetic mineral in certain 
basic igneous rocks, 

Typical analyses of the four varieties of biotite follow. 



Si0 2 
Ti0 2 
A1 2 3 



I 


n 


HI 


IV 


40 81 


35 79 


32 35 


39 66 




3 5i 


tr 


56 


16 47 


13 70 


17 47 


17 co 


2 16 


4 04 


24 22 


27 


s 92 


17 09 


13 II 


20 




40 


I. 2O 





FeO 

MnO. 

CaO i 48 

BaO 33 62 

MgO 21 08 9 68 89 26 49 

Na 2 i 55 45 7 oo 60 



ANHYDROUS ORTHOSILICATES 351 

I II III IV 

K20 9 01 8 20 6 40 9 97 

H 2 0- \ 90 I , 66 

H 2 0+ I 219 3*6 I* 6 ' 233 

F 10 2 24 

(lessO=F) 99 19 99 91 100 83 99 66 

I Anomite from Greenwood Furnace, Orange Co , N Y 

II Meroxene from granite, Butte, Mont 

III Lepidomelane from eleohte syenite Litchfield, Maine 

IV Brown phlogopite from Burgess, Can 

Before the blowpipe the dark, ferruginous varieties fuse easily to a 
black glass, the lighter colored varieties with greater difficulty to a 
yellow glass Their powder reactions are strongly alkaline The 
minerals are not attacked by HC1 but are decomposed by strong 
EfeSO* In the closed tube all varieties give a little water 

The biotitcs are distinguished from all other minerals except the other 
micas by perfect cleavage and from other micas by their color, solubility 
in strong sulphuric acid and pleochroism 

The commoner alteration products of biotite are a hydrated biotite, 
chlorite (p 428), epidote, sillimamte and magnetite, if the mica is 
ferriferous At the same time there is often a separation of quartz 
Phlogopite alters to a hydrophlogopite and to penmnite (p. 429), and 
talc (p 401) 

Syntheses The biotites are common products of smelting operations. 
They have been made by fusing silicates of the proper composition with 
sodium and magnesium fluorides 

Occurrences and Origin The biotites are common constituents of 
igneous and metamorphic rocks and pegmatite dikes They also are 
common alteration products of certain silicates, such as hornblende 
and augite They are present m sedimentary rocks principally as the 
products of weathering 

Uses Phlogopite is used as an insulator in electrical appliances 
and to a less extent for the same purposes as those for which ground 
muscovite is employed No "amber mica" is produced in the 
United States Most of that used in this country is imported from 
Canada. 



352 DESCRIPTIVE MINERALOGY 

THE CALCIUM MICAS 

Margante (Ca(AlO) 2 (AlOH) 2 (SiO4)2) 

Margante, the calcium mica, is like biotite in the habit of its crys- 
tals, which, however, are not so well formed as these Usually the min- 
eral occurs in tabular plates with hexagonal outlines but without side 
planes It occurs also as scaly aggregates 

Analyses of specimens from Gamsville, Ga (I), and Peekslull, N Y 
(II), gave 

Si0 2 A1 2 3 FeO MgO CaO Na 2 H 2 Total 

I 31 72 50 03 12 ii 57 2 26 4 88 100 58 

II 32 73 46 58 5 12 i oo ii 04 4 49 100 96 

The mineral has a pearly luster on its basal planes, and a glassy luster 
on other planes Its color is while, yellowish, or gray and its streak 
white It is transparent or translucent Its cleavage is not as perfect 
as in the other micas, and its cleavage plates are less clastic Its hard- 
ness vanes from 3 to over 4 and its density is 3 It is a mica of the 
first order 

Before the blowpipe it swells, but fuses with great difficulty It 
gives water m the closed tube and is attacked by acids 

Occurrence Margante is associated with corundum It is also 
present in some chlorite schists In all cases it is of mctamorphic origin 

Localities It occurs in the Zillerthal, Tyiol, at Campo Longo, m 
Switzerland, at the emery localities m the Grecian Archipelago, at 
the emery mines near Chester, Mass , in schist inclusions in mica 
dionte at Peekskill, N Y , with corundum at Village Green, Penn , 
at the Cullakenee Mine, in Clay Co , N. C, and at corundum local- 
ities in Georgia, Alabama and Virginia 

THE LITHIUM-IRON MICAS 

Zinnwaldite ((Li- K- Na) 3 FeAl(Al(F- OH)) 2 Si 5 Oi ) 

The pnncipal hthmm-iron mica, zmnwaldite, is a very complex 
mixture that occurs m several forms so well characterized that they have 
received different names All of them contain lithium, iron and fluorine, 
but in such different proportions that it has not been possible to ascribe 
to them any one generally acceptable formula Some of the most im- 
portant of these varieties have compositions corresponding to the fol- 
lowing analyses 



ANHYDROUS ORTIIOHILK'ATES 353 

I IT III IV 

Si0 2 . 40 19 59 25 s 1 46 45 87 

22 79 12 57 l6 22 22 $O 

19 78 2 21 66 

FeO 93 7 66 ii 6r 

MnO 2 02 06 i 75 

NasO 7 63 95 42 

K 2 7 49 5 37 I0 6 5 10 46 

Li 2 3 06 g 04 4,83 3 28 

F 3 99 7 3^ 7 44 7 94 

Total 99 32 102 ii 102 71 105 48 



0=F= 97 64 99 05 99 60 102 15 

I Rabenghmmer from Altenberg Saxony Greenish black with greenish gray 

streak Sp gr =3 146-3 IQO 

II Polyhlhiomlc from Kangerluarsuk, Greenland White or light green plates 
Sp gr =281 

III Cryophyllitc from Rrxkporl, Mass, Strongly plewhroic green and brown- 

ish led crystals Sp gr 2 QOQ Contains also 17 MgO and i 06 HgO 

IV Zinnwaldile from Zmnwald, Bohemia. Plates, white, yellow or greenish 
gray Sp. gr =2 956-2,087 Contains also r;i IIjO and 08 



Zinnwalchle occuis m crystals with u,n axial ratio very near that 
of biotitc, and a tabular habit Twins arc like those of biotitc with 
ooP(iio) the twinning plane 

It has a pearly luster, is of many colors, particularly violet, gray, 
yellow, brown and dark gieen and is strongly plcochroic. Its streak is 
light, Us hardness between 2 and 3 and its density between 2.8 and 3 2. 
It is a mica of the second 01 der 

Before the blowpipe it fuses to a dark, weakly magnetic bead It is 
attacked by acids 

Qccumnte and Lotahtic\ Zmnwaldite is found m certain ore veins, 
m granites containing cassiterite, and m pegmatites Its origin is as- 
cribed to pneumatolytic processes Us principal occuirences are those 
referred to m connection with the analyses 

TU& ALKALI MICAS 

The alkali micas include those m which the principal metallic con- 
stituents besides aluminium are lithium, potassium and sodium. All 
these metals are present in each of the recognized varieties of the 
alkali micas, but in each variety one of them predominates That in 
which lithium is prominent is known as lefodolite; that m which potas- 



364 DESCRIPTIVE MINERALOGY 

sium is most abundant is muscowte, and that in which sodium is 
most prominent is paragomte Muscovite is common Lepidolite is 
abundant in a few places Paragomte is rare The first two are im- 
portant economically All are micas of the first order, except a few 
iepidolites, and all are light colored 

Another mica, which is usually regarded as a distinct variety of 
muscovite, or, at any rate, as being very closely related to the mineral 
is roscoelite In this, about two-thirds of the AlgOs m muscovite is 
replaced by VgOj, It is a rare green mica which is utilized as an ore 
of vanadium, 

Lepidolite ((Li- K-Na) 2 ((Al-Fe)OH) 2 (SiO,Oa) 

Lepidohte occurs almost exclusively as aggregates of thin plates 
with hexagonal outlines Crystals are so poorly developed that a satis- 
factory axial ratio has not been determined Its variation m composi- 
tion is indicated by the analyses of white and purple varieties from 
American localities 

Si0 2 
A1 2 3 



I 


II 


III 


IV 


51 52 


49 52 


5* 12 


51 25 


25 96 


28 So 


22 70 


25 62 


31 


40 


80 


12 


undet. 


24 , 




OO 


20 


07 


I 34* 


s 


02 


02 




OO 


16 


13 




tr 


4 9 


3 87 


S 12 


4 3* 


i 06 


13 


2 28 


T 94 


11 01 


8 82 


10 60 


10 65 


. 


3 73 








08 




. * 


5 So 


S 18 


638 


7 06 


95 


i 72 


2 Og 


i 60 



FeO 

MnO 

MgO 

CaO 

LiaO 

NaaO 

KsO 

Rb 2 

CsaO. 

F. 

BfeO 

Total 

(lessO=F) 99 45 100 53 99 74 99.63 

I. Like-purple granular lepidohte from Rumford, Maine 
II White variety from Norway, Maine 
III Red-purple variety from Tourmaline Queen Mine, Pala, Cal. Contains 

also 04 PjOj 
IV. White variety from Pala, Cal 

*Mn0 8 



ANHYDROUS ORTHOSILICATES 355 

The mineral is while, rose or light purple, gray or greenish The 
rose and purple varieties contain a little manganese The streak 
of all lepidolites is white, their luster pearly, their hardness 2 5-4 
and density 28-29 The refractive indices of a typical variety are 
0=i 5975* 7 ==16047 

Lepidohte fuses easily to a white enamel and at the same time colors 
the flame red It is difficultly attacked by acids, but after heating is 
easily decomposed 

Cookeitc fiom Maine and California is probably a weathered lepido- 
hte Its analyses concspond to the foimula, Li(Al(OH)2)3(SiOa)2 

Occutrencc The mincial occuis puncipally in pegmatites in which 
lubelhte (p 435), and other bi ight-colored tourmalines exist and on 
the borders of granite masses and in rocks adjacent to them It is 
often zonally mtergrown with muscovitc In all cases it is probably a 
pncunutolytic pioduct, or, at least, is produced by the aid of magrnatic 
emanations 

Localities The mineral occurs in nearly all districts producing tin, 
and also in those producing gem tourmaline Its best known foreign 
localities are Jekatcrmbuig, Russia, Rozna, Moravia, Schmttenhofen, 
Bohemia, and Penig, Sa\ r on> In the United States it is found in large 
quantities at Hebron, Pans, and other points in western Maine, m the 
tin mines of the southern Black Hills, South Dakota, and in the tourma- 
line localities m the neighborhood of Pala, San Diego Co , Cal 

Usei> Lepidohte is utilized to a slight extent m the manufacture of 
lithium compounds, which are employed m the preparation of lithia 
waters medicinal compounds, salts, used in photography and m the 
manufacture of fireworks and stoiage batteries 

Muscovite (H a (K Na)Alj(SiOi)a) 

Muscovitc is one of the most common, and at the same time the 
most important, of the micas Because of its transparency it is em- 
ployed for many purposes for which the darker biotite is not suitable 

While predominantly a potash mica, nearly all muscovite contains 
some soda, due to the isomorphous mixtuie of the paragomte molecule. 
Two typical analyses are quoted below: 



Si0 2 AlsOs FeaOs FeO MnO MgO CaO Na a O K S H a O F Total 

I 44 39 35 7 * 09 i 07 tr ro 2 41 9 77 5 88 .72 10113 

II. 46 54 34 96 i 59 . 32 4* *o 38 5 43 99 63 

I. Broad plates of muscovite bordered by lepidoiite, Auburn, Maine. 
II Greenish muscovite, Auburn, Maine Total less QF n 100.83 



356 



DESCRIPTIVE MINERALOGY 



The crystals are usually tabular and frequently orthorhombic or 
hexagonal in habit, though the etch figures on their basal pknes reveal 
clearly their monoclimc symmetry (Fig 194) If onentated to corre- 
spond with crystals of biotite their a\ial constants are a b c== 5774 
i . 3 3128, 0=89 54', and their principal planes oP(ooi), oo p & ( O io) 
|P ob (023), 4P(44i) and -2P(22i) (Fig IQS) 

Twins like those of biotite are not uncommon in some localities 
Muscovite is colorless or of some light shade of green, yellow or red 
It has a glassy luster, a perfect cleavage parallel to the base, a haidness 
of 2 and a density of 2 76-3 i Pleochroism is marked in dncctions 
perpendicular and parallel to the cleavage, the color of the crystals, 
when viewed in the direction perpendicular to the cleavage being lighter 




FIG 194 



I'll, 1 1)5. 



FIG 194 Etch Figures on oP(ooi) of Muscovite, Exhibiting Monodmu, Symmetry 
FIG 195 Muscovite Crystal with 2P, 221 (Af) t oP, ooi (<), <wPw, oio (/;), 

and 3P>, 023 (r) 



than when viewed parallel to the cleavage The optic al angle is com- 
paratively large (56-76), in this respect being vciy different from that 
of biotite which is small (2-22) The mineral is a nonconductor 
of electricity at ordinary temperatures and a poor conductor of heat. 
Its refractive indices vary somewhat with composition For yellow light 
intermediate values are as follows a~ i 5619, j8- 1.5947, 7= 1,6027, 

Before the blowpipe thin flakes of muscovite fuse on their edges to a 
gray mass In the dosed tube the mineral yields water which, in some 
cases, reacts for fluorine It is insoluble m acids under ordinary coi> 
ditions, but is decomposed on fusion with alkaline carbonates. 

Muscovite is very stable under surface conditions Its principal 
change is into a partially hydrated substance, which may be culled 
hydromuscovite. It alters also into scaly chlontic products, into 
steatite (p 401), and serpentine (p, 398). 



ANHYDROUS ORTHOSILICATES 357 

DomounU is a dense fine-grained aggregate of muscovite, often 
forming pseudomorphs after other minerals 

Senc^te is a yellowish or greenish muscovite that occurs in thin, 
curved plates m some schists 

Fwhsite is a chromiferous variety of an emerald-green color from 
Schwarzenstem, Tyiol 

Synthesis Crystals of muscovite have been made by fusing anda- 
lusite with potassium fluo-sihcate and aluminium fluoride 

Occurrence Muscovite occurs in large, ill-defined crystals in peg- 
matites, and in smaller flakes in giamtes and othci acid igneous rocks, 
in some sandstones and slates and m various schists and other meta- 
morphic rocks It is found also in veins It is m some cases an orig- 
inal pyrogemc mineral, m other cases a mctamorphic mineral and m 
still other cases a sccondaiy mineral resulting from the alteration of 
alkaline aluminous silicates 

Localities The mineral occurs m all regions where pegmatites and 
acid igneous rocks c\ist It is mined m North Carolina, South Dakota, 
New Hampshire, Virginia and other states While phlogopitc (amber 
mica) is produced in some countries all the mica produced in this country 
is of the muscovite variety 

t/iw Muscovite is used m two forms, (i) as sheet mica, and (2) 
as ground mica. The sheet mica comprises thm cleavage plates cut 
into shapes It is used in making gas-lamp chimneys, lamp shades, and 
windows in stoves. The greater portion is used as insulators m 
electrical appliances, though for some forms of electrical apparatus the 
amber mica js better Because of the comparatively high cost of large 
mica plates, small plates are sometimes built up into larger ones The 
ground mica consists of small crystals and the waste from the manu- 
facture of sheet mica giound very fine. It is used in the manufacture 
of wall paper, heavy lubucants and fancy paints It is also mixed with 
shellac and melted into desired forms for electrical insulators 

Production The total value of the mica produced in the United 
Stales during 1912 was $355,804, divided as follows. 1,887,201 Ib sheet 
mica, valued at $310,254 and 3,512 tons ground mica, valued at $45,550 
Of this North Carolina produced 454,653 11), of sheet mica, valued at 
$187,501 and 2,347 tons of scrap mica, valued at $29,798, or a total 
value for both kinds of mica of $217,299 The imports of sheet mica 
during the same year amounted to $502,163, of which 241,124 Ib , 
valued at $155,686 was trimmed and the balance untnmmed The 
imports during 1912 were valued at $748,973, and the domestic produc- 
tion at $331,896- 



358 DESCRIPTIVE MINERALOGY 

Roscoelite may be regarded as a muscovite in which a large portion 
of the AkOs has been replaced by V 2 0s A specimen from Lotus, Eldo- 
rado Co , Cal , gave 

Si0 2 Ti0 2 A1 2 3 V 2 3 FeO MgO K 8 H,0- H,0+ Total 
45 17 78 ii 54 24 01 i 60 i 64 10 37 40 4 29 99 80 

besides traces of Li20 and Na20 

The mineral occurs as clove-brown or green scales with a specific 
gravity of 2 92-2 94 It is translucent and has a pearly luster and a 
strong pleochroism. Its refiactive indices for sodium light are, <x= 1,610, 

0=1685,7=1 704 

Before the blowpipe it fuses to a black glass. It gives the usual 
reactions for vanadium m the beads and is only slightly alTccted by 
acids It has been found associated with gold m small veins ncui Lotus, 
Eldorado Co., California, in seams composed of roscochte and quartz 
between the beds of a sandstone in the high plateau region of south- 
western Colorado, and as a cement of minute scales between the grams 
of the sandstone on both sides of the seams. In all cases it appears to 
have been deposited by percolating water, possibly of magmatic origin 

The impregnated sandstone is mined as a source of vanadium The 
material, which contains an average of about 3 per cent of metallic 
vanadium is concentrated by chemical processes, and the concentrates 
are manufactured into ferro-vanadium. Most of the vanadium pro- 
duced in the United States is made from this ore, 

Paragonite ^(Na-KJAlsCSiO-Oa) 

Paragonite, the sodium mica, differs from muscovite mainly in com- 
position Both contain sodium and potassium but in puragomte the 
sodium molecule is in excess 

The analysis quoted below is made on a sample from Monte Cam- 
pione, in Switzerland 

Si0 2 AI 2 3 Fe 2 3 Na 2 K 2 H 2 Total 
47 75 40 10 tr. 6 04 i 12 4 58 99 59 

It occurs in the same associations as some forms of muscovite but it 
is much less common. It apparently occurs most abundantly in certain 
fine-grained mica schists to which the name paragonite schists has been 
given, It i m ail known cases a product of dynamic metamorphism* 



CHAPTER XVII 
THE SILICATES-Cowfowwrf 

THE ANHYDROUS METASILICATES 

NORMAL METASILICATES 

Beryl (Be a Al 2 (Si0 3 )o) 

BFRYL is a frequent constituent of coarse-grained granites. It is 
important as a gem matciial, and is particularly interesting because of 
the many physical investigations that have been made with the aid of its 
crystals 

Although the mineral is essentially a beryllium alummo-rnetasilicate, 
it usually contains also a little FesOa and MgO, in many cases small 
quantities of the alkalies, and in some cases also caesium. Analyses of 
a green beryl from North Carolina, an aquamarine from Stoneham, Me , 
and a light-colored crystal from Hebron are given below 



Si0 2 AfcOi Fe 2 0;j BeO FeO Na 2 Li 2 Cs 2 H 2 Total 

I. 66 84 19 05 . 14 n . ....... 100 oo 

II. 66 28 18 60 . 13 61 ,22 ,, ,. .83 90 54 

III 65 54 17 75 21 13 73 71 ... 2 01 100 39 

IV, 62 44 17,74 40 ii 36 ,38 i 13 I 60 3.60 2.03 100 30 

I Theoretical 
II, Alexander Co,, N. C, 
II I Stoneham* Me.; ako.o6%CaO. 
IV, Hebron, Me 

The mineral occurs massive without distinct crystal form and also in 
granular and columnar aggregates, but its usual method of occurrence is 
in sharp and, in some cases, very large columnar crystals with a distinct 
hexagonal habit (dihexagonal bipyramidal class), and an axial ratio 
i : 4989. The forms found on nearly all crystals are oo P(tolo), 
ooP2(ii2o), oP(oooi), P(ion), P2(ii22) and 2P2(ii2i) (Fig 196), 
In addition, there are present on many crystals other prismatic forms 
and the pyramids 3?f (2131) and aP(ao3i). Other crystals are highly 

359 



360 



DESCRIPTIVE MINERALOGY 



modified (Fig 197), the total number of forms that have been identified 
approximating 50 The angle icli Aoi7i = 28 55' Some crystals 
are very large, measuring 2 to 4 feet in length and i ft in diameter 

Beryl has a glassy luster It is transparent or translucent It is 
colorless or of some light shade of green, red, or blue Its streak is 
white, hardness 7-8 and density 2 6-2 8 Its cleavage is very imperfect 
but there is frequently a parting parallel to the base Pleochroism is 
noticeable in green and blue crystals Its refractive indices for yellow 
light at 20 are co= i 5740, e= i 5690 They become greater with increas- 
ing temperature 

Before the blowpipe colorless varieties become milky, but others are 





FIG tg6 1'ic, 197 

FIG 196 Beryl Crystals with op, ioTo (w), oP oooi (c), < P2, 1120 (a), P, 
loii (p) and 2?2, 1 121 00 

FIG 197 Beryl Crystal with m, c, p and A as m Fig 196 Also 2p, 202 1 (M) and 

3Pg, 2131 M 



unchanged except at very high temperatures when sharp edges arc fused 
to a porous glass The mineral is not attacked by acids. 

Beryl is distinguished from apatite, which it much resembles, by its 
greater hardness 

It alters to mica and kaolin (p 404) 

Syntheses Beryl crystals have been formed by long heating of 
8162, AkOs and BeO m a melt of the molybdate or vanadate of lithium, 
and by precipitating a solution of beryllium and aluminium sulphates 
with sodium silicate and heating the dried precipitate with boric acid 
in a porcelain oven 

Occurrence The mineral occurs as an accessory constituent m peg- 
matites and granites, in crystalline schists, especially mica schists and 



ANHYDROUS METASILICATES 361 

gneisses, m ore veins and sometimes in clay slates and bituminous lime- 
stones 

Uses The transparent varieties are utilized as gems, under the 
following names 

Emerald is a deep green variety, the color of which is probably 
due to CroOa, 

Aquamarine, a blue-giccn variety, 

Golden beiyl, a topa/-coloiecl variety, 

Blue betvl, a blue vanety, and 

White beryl, a coloiless variety 

Localities Crystals of ordinal y ber>l occur at Stnegau, Silesia, in 
the cassitente veins near Altcnbcrg, in Savony, m the granite dikes near 
S Piero, Elba, in the Mouine Mts , at Down, Ireland, at various points 
(especially near Jekatermburg), in Uuil, Russia, and in North America, 
m the mountain counties of Noith Carolina; at Mt. Antero, Colo ; at 
Peiperville, Pcnn , in giamte veins at Haddam, Conn., at Acworth, 
N H , and at Norway, Hebron, and other points in western Maine 
Much of the beryl of Maine is the variety containing caesium. 

The finest emeralds are found in geodes, and embedded in a clay 
slate at the Muso Mine, Colombia, New Grenada, but fine gem mate- 
rial occurs also at Zabara, neat the Red Sea, Habachthal, Tyrol, Glen, 
New South Wales, and m Bnuil, Hindustan and Ceylon. The finest 
aquamarines come from Sibeiia, 

The most important beryl mines m the United States are m pegma- 
tites in Cleveland, Burke and Macon Counties, N C Aquamarine, 
golden beryl and the more usual varieties occur at Walker Knob, Burke 
Co , and on Whiterock Mt in Macon Co., but those at the first-named 
locality are not clear enough to furnish gems. Near Clayton, Ga , a 
pegmatite contains large bliush and yellowish green beryls, some of which 
yield gem material The finest aquamarine ever found m the United 
States was from Stoneham, Me. Near Shelby, Clevelaid Co , and at 
Crabtree Mountain, Mitchell Co , m North Carolina, genuine emeralds 
occur in a pegmatite that cuts basic rocks. Fine emeralds have also 
been mined at Stony Point, N C,, Haddam, Conn., and Topsham, Me 

Production The total yield of emerald from North Carolina during 
1912 was about 2,969 carats, valued at $12,875 in the rough The 
average value of the cut stone was $25 per carat, but some especially 
fine gems from the Shelby locality were valued at $200 per carat There 
were also produced in the United States during this year other varieties 
of beryl, valued at $1,765. 



362 DESCRIPTIVE MINERALOGY 

Leucite (K 2 Al2(SiO 3 )4) 

Leucite occurs almost exclusively m what are apparently simple 
isometric crystals, but which are actually polysynthetic twins of a doubly 
refracting substance At 500 and above, leucite substance is isometric. 
It separates from molten magmas as isometric crystals, which, upon 
further cooling, become twinned The twinning is revealed by striation 
on the crystal faces The substance is, therefore, dimorphous 

Theoretically, leucite is a potassium aluminium meUsihcate, but 
most natural crystals contain some soda and many contain small quan- 
tities of calcium The calculated composition of the pure molecule and 
the actual composition of two natural crystals are shown below 

Si0 2 A1 2 3 CaO Na 2 K 2 O HjO Total 

Calculated 55 02 23 40 21 58 100 oo 

Mt Vesuvius ss 28 24 08 60 20 79 100 75 

Mt Vulture 54 94 25 10 i 80 i 23 15 18 2 13 100 38 

The mineral occurs in icositetrahedrons, 262(211), m some cases 
modified by oo 0(no) and oo oo (100) Twinning parallel to oo 0(no) 
is common, but often the twins are polysynthetic and are recognizable 
only by stnations on the crystal faces The twinning lamellae are 
amsotropic, as shown by their optical properties, but at 500 the twin- 
ning disappears and the crystals become completely isotropic through- 
out 

Leucite is glassy in luster and colorless, white or light gray m color. 
It is transparent or translucent and has a white streak. Its cleavage is 
imperfect parallel to oo 0(no), and its fracture is conchoidal or unevt k n. 
It is brittle Its hardness is 5-6 and density 2 5. Its indices of refrac- 
tion approximate i 508 

Before the blowpipe leucite is infusible It is soluble m HC1 with 
the production of pulverulent silica Its powdei reacts strongly alka- 
line 

It is distinguished from other minerals by its crystallization, by the 
violet color it imparts to the flame and its reaction toward HCl, It is 
most apt to be confused with analcite (p, 458) and colorless garneL It 
is distinguished from the latter by its inferior hardness and from the 
former by its mfusibility and failure to yield water when heated in the 
glass tube below red heat Analcite, moreover, fails to give the flame 
test for potash 

The mineral alters quite readily into analcite and some other zeolite, 
into a mixture of orthoclase and nepheline, or into orthoclase (p. 413) 



ANHYDROUS METASILIOATES 



363 



and muscovite, or into orthoclase alone* Its final alteration product is 
kaolin 

Syntheses Us crystals have been obtained by fusing its constituents, 
and also by molting a mixture of SiOa, potassium alummate and vana- 
date, and by fusing a mixtuic of Si(\> and Al^O* with an excess of KF 

Occurrence It occurs only in igneous rocks, especially m lavas low in 
silica and high m potash, and in the plutomc rock known as missourite 
In some old rocks it is repie&ented by its alteration products. In all 
cases it is a pimuiy mineral 

Localities Leucite is an essential constituent of the lavas m the 
Kaiserstuhl, Baden, m Rhenish Prussia, near Wiescnthal, Saxony, 
in the Sicbcnburgei, Bohemia; at Vesuvius, Italy, m the Leucite Hills, 
and other places in Wyoming, and at several places in Montana, at 
Magnet Cove, Ark , and near Hamburg, N J 

VMS. It is suggested that the large masses of leucitc rocks m the 

Leucite Hills be used as a source of potash On the assumption that 

the rocks at this place contain ro ]>er cent of K^O it is estimated that 

the total quantity of potash in them amounts to about 200,000,000 tons. 



THE AMPHIBOLOUS 

The amphibolous embrace a large numbei of minerals, some of 
which are extremely important as lock components. Economically, 



^-T~^\Ji 
pio 

^110 

100 ~ 



Jio 






110 



uo 



B 




FIG. ig8 Cross-Sections, of Pyroxene (A) and Amphibolc (#) Crystals* Illustrating 
Differences in InterseUionb of Cleavage* 

they have little value. Several are used iri the arts, but only to a com- 
paratively slight extent. Apparently they crystallize in the orthorhom- 
bic, monoclimc and triclmic systems. 

The amphiboloids are divisible into two groups, the pyroxenes and 
the amphtboles, which differ from one another in the ratio between their 



364 DESCRIPTIVE MINERALOGY 

a and b axes. In the pyroxenes this ratio is nearly i . i, while in the 
amphiboles it is approximately 2 i The angle between the prismatic 
planes ( oo P, no) on the former is nearly equal (87 and 93), and on 
the latter very unequal (s6-i24). Since, moreover, in all members of 
both groups there is a distinct cleavage paiallel to the unit prism, the 
angles of intersection of the cleavage planes in the pyroxenes and in the 
hornblendes are also different This difference m prismatic and cleav- 
age angles of the two groups serves leadily to distinguish between them 
(Fig 198) 

The pyroxenes appear to be the more stable at high temperatures 
and the amphiboles under high pressuies Thus pyroxenes are more 
common than the amphiboles in lavas and amphiboles more common 
than pyroxenes in crystalline schists 

Chemically, the amphiboloids are metasihcates ot Na, Li, Mg, Ca, 
Fe, Mn, Zn and Al, or isomorphous mixtures of Ihcse metasihcates with 
one another and with an orthosilicate of the general composition rep- 
resented by (Mg Fe)((Al Fe)O) 3 SiQi 

THE PYROXENES 
(R"Si0 3 , R'Al(Si0 3 ) 2 and RVoVSiO,) 

The pyroxenes occur very widely spread as constituents of igneous 
rocks, and in veins that have been filled by igneous processes. Some 
members of the group are also common metamorphic pi oducts Although 
crystallizing in different systems their crystals possess a ccitam family 
resemblance, expressed best in their hon/ontal cross-sections, which 
have a nearly orthorhombic symmetry, i e , they uic nearly symmetrical 
about two planes at right angles to one another, passing through the 
a and b axes, which are nearly equal The most perfect cleavage of all 
the pyroxenes is parallel to ooP(no), and consequently their cleavage 
angles aie nearly equal (Fig I98A) They approximate 92 and 88, 
with the plane of the a and c axes (the plane of symmetry in monochnic 
forms) bisecting the acute angle 

The best known members of the series with their axial ratios are 
listed below In the case of the orthorhombic members it will be noticed 
that the shorter of the lateral axes is made x This is clone to empha- 
size the correspondence between the orthorhombic, monoclimc and tri- 
chmc forms in their axial ratios The usual orientation, that which 
regards the longer of the lateral axes as 5(=i) gives a : b . c 9702 
: i : 5710 for bronzite, and .9713 : i 5700 for hypersthene. By 
many authors wollastomte and pectolite are placed in an independent 



ANHYDROUS METASILICATES 



365 



group partly because of the fact that they are much more easily decom- 
posed by acids than are the other pyroxenes, and partly because of 
their very different crystal habits, and different axial ratios 



Orlhorhombic (possibly twinned monochmc) 

MgSiO b a c =* i oss i 587 

(Mg Fe)SiO, =10308 i 5885 



Bronzite 
Hypersthene 



Wollaslomtc 

Peclohte 

Diopside 

Sahhte 

Hedcnbcrgite 

Schejfente 

Aiigile 

Acmite 
Aeginnc 

fadcitc 
Spodumene 



Rhodonite 
Bu\tamtte 
Rabmglonite 
Fowlente 



FcSiOj 



1 02QS r 5868 



Monoclimc (monochmc prismatic class) 



CaSiO, 

HNaCa2(Si0 3 ) 3 

(Mg Gi)SiO, 

(Mg Fc)Ca(Si0 8 )2 

FeCa(SiO n )2 

(Mg Fc)(Ca Mn)(SiO,)i 
r(Mg PeJCXSiCMj 
I (Mg Fc)((M Fc)0)jSi0 4 
lNd(Al Fc)(biOOa 



a b c i 0523 i 9649 0=8 
=1 1140 i 9864 
10921 i 



\ (M Fe)((Al 
Na\l(SiO,)j, 
LiAl(SiO,)> 



,0.) 



i OpO 



= 10955 



= 1090-6 
i oqS 



1283 



5893 
S83 

5904 
6012 



613 
6234 



=84 40' 
= 74 ' 

=74 10' 



= 74 14' 

= 73 ii' 
= 7? 09' 



Trichnic (trichnic piiucoidal ckiss) 

MnSiOi a I '6=1 0729 i 6213 108 44' 

(Mn Ca)SiOi 

(Ca Fe Mn)jFcfc(SiOOi =10807 i 6237 ^saio834' 

(Mn Fc Ca Zi 



In addition, there arc several comparatively rare monoclimc pyrox- 
enes and one trichnic form, that contain zirconium. They occur only 
as components of rocks rich in alkalies. 



PYROXENES 

Enstatite (MgSiOa) Bronzite Hypersthene (FeSiO 3 ) 

The orthorhombic pyroxenes are isomorphous mixtures of MgSiOa 
and FeSiOs The pure magnesium and iron molecules are not known in 
nature, though the former has been produced artificially. Nearly all 
members of the group contain both magnesium and iron. When the 
proportion of the iron present is small (5 per cent FeO), the mixture is 
known as ewtotite Mixtures with 5 to 16,8 per cent of FeO (cor- 



366 



DESCRIPTIVE MINERALOGY 



responding to MgO . FeO =3 Z X are known as bronzite and mixtures 
containing more than 16 8 per cent FeO are known as hypersthene 
The composition of MgSiOs and of some typical members of the group 
follow 



Si0 2 

I 60 03 

II 58 oo 

HI 55 So 

IV 52 12 



A1 2 3 FeO 



35 



i 69 



3 16 
16 80 
20 94 



MgO 

39 97 
36 91 
27 70 
21 56 



CaO HaO 



80 



3 20 



Total 
100 oo 

100 22 
100 00 

99 Si 



I Calculated composition of MgSi0 3 
II Portion of large crystals of enstatite from Kjorrestad, Norway 

III Calculated composition of upper limit of bronzite, i c , m which MgO FeO 

=3 i 

IV Hypersthene powder separated from a gabbro at Mt Hope, Md 

The three minerals occur in crystals that have a well marked ortho- 
rhombic symmetry, but it is believed that this may be a case of pseu- 
dosymmetry only, i e , that the minerals may in reality be monochnic, 
and that their apparently orthorhombic symmetry may be due to 
repeated polysynthetic twinning of very thin lamellae. Monochnic 
MgSiOs has been made by fusion of Si02 and MgO in the presence of 
B20a, but it is not certain that this is identi- 
cal with an iron-free enstatite 

The natural crystals of the oilhorhombic 
pyroxenes are columnar in habit and are 
usually bounded by oo P(no), oo P 06(010), 
oo P 66(100), P2(2i2), JP 06 (014), with the 
addition on some crybtals of 001*2(120), 
|P 56 (034), P(iii), aP5(an), iP*(o) 
and other forms (Fig 199) All cleave per- 
fectly parallel to ooP(uo) with u cleavage 
angle of 88 i6'-2o' and 91 4o'~44'* The 
angle noAiIo=88 16' to 88 20'. 

The color and other physical properties of 
the orthorhombic pyroxenes vary with the 

amount of iron present Enstatite is light gray, yellow or green. 
Hypersthene is black, dark purple or dark green Bronzite is brown, 
or some shade lighter than hypersthene and darker than enstatite. 
All colored varieties are pleochroic, the difference in color in different 
directions increasing with the increase in iron Green, red, yellow and 
brown tints are most prominent. All varieties have a colorless streak. 



FIG. 199 Enstatite Crys- 
tal with oo P, no (m), 

oo Poo, 100 (a), oo Poo, 
oio (6), |P co, 023 (q), 
JPoS, 012 (*), |P5, 
016 ($) and |P, 223 (T) 



ANHYDHOUH METASILICATES 367 

Many hypcisthencs and bronzites exhibit a metallic shimmer on 
oo P 06(010), due to tiny inclusions with then flat sides parallel to 
this direction The hardness of the orthorhombic pyroxenes vanes 
between 5 and 6 and then density between 3 i and 3 5 increasing with 
the iron present Their refractive indices for yellow light are 

Enstatite a i 665 /3=i 669 7=1 674 

Hypersthene =i 692 =i 702 =i 705 

Before the blowpipe the iron-free members of the series are infusible. 
With increase m iron they become more easily fusible, very ferruginous 
hypersthene melting easily to a greenish black weakly magnetic glass 
When treated with hydrochloric acid the members near enstatite are 
unattacked, while those near hypersthene are slightly decomposed 

Syntheses Crystals of these pyroxenes have been made by fusing 
the proper components with BaOj), and by heating mixtures of SiCfe and 
MgCfe They are frequent constituents of slags 

Occurrence The rhombic pyroxenes occur in igneous rocks, in crys- 
talline schists, m metamorphosed dolomites and in veins that have been 
filled by igneous magmas They are not very stable under the condi- 
tions at the earth's surface They weather to serpentine, hornblende 
and rarely to talc Enstatite occurs also m meteorites 

Locahhe^ Good crystals of the orthorhombic pyroxenes are found 
in the volcanic bombs (inclusions m lava) of the Lake Laach district, 
Prussia, in oie veins at Bodenmais, Bavaria, at Mlnds, Hungary, 
m the trachyte of Mont Dore, France, in apatite veins at Snarum, 
Norway, and in a glassy andesite on Peel Island, Japan In the United 
States they occur m basic coarse-grained igneous rocks m North Carolina, 
Maryland, and the Highlands of New York and New Jersey, m volcanic 
rocks in Colorado, and at the Corundum Mines, m Georgia. Espe- 
cially fine bronzite occurs on Paul's Island, Labrador. 

MONOCLINIC PYROXENE'S 

The monoclinic pyroxenes comprise a series of isomorphous mixtures 
of monoclinic mctasihcutes of Na, Li, Ca, Mg, Fe" and Mn and the 
silicate R" (R"'0)a Si0 4 , in which R" is usually Mg, Ca or Fe and R'" 
is Al or Fe. 

.Although their chemical composition vanes quite widely, the crys- 
tallization of all the members of the group is practically the same With 
the exception of wollastomte and pectolite the habit of their crystals is 
similar and their corresponding mterfacial angles have approximately 
the same value. 



368 DESCRIPTIVE MINERALOGY 

The group may be subdivided into four subgroups (i) the wollas- 
tonite subgroup, including this mineral and pectolite, with calcium as 
the principal metallic component, (2) the magnesmm-calcium-iron 
pyroxenes, including diopside, sa\hte, lelenbergite and augtte, and (3) 
the alkali pyroxenes including acm te,jaleite and *po lumene A fourth 
subgroup includes the rare zirconium-bearing pyroxenes All crystal- 
lize in the monoclinic prismatic class 

WoUastomte Subgroup 

These minerals, because their axial ratios are somewhat different 
from those of the other monoclinic pyroxenes, and because they are 
much more easily decomposed by acids, are by some mineralogists re- 
garded as constituting an independent group 

Wollastonite (CaSiOs) 

WoUastomte analyses correspond very closely to the theoietical 
composition required by the formula assigned to it There is, however, 
nearly always a little Fe20a present and usually there arc present also 
small traces of other constituents A dimorph, pseudowollastonite, 01 
/3 wollastomte, has been made by melting wollastomtc and cooling 
slowly, but it has not yet been found m nature Its crystals arc hexag- 
agonal or monoclinic with an hexagonal habit 

Si0 2 FeO MnO CaO MgO Na 2 H 2 Total 

Theoretical 51 75 48 25 . 100 oo 

Bonaparte Lake, N Y 50 66 07 47 98 05 46 72 99 94 

The mineral forms tabular or columnar crystals bounded by 
oo P 60(100), -Poo(ioi), oP(ooi), P6o(io7), oop2(i2o), -PS(i22) 

and oop|(54o) (Fig 200). Twins are 
sometimes found with oo P 6b (100) the 
twinning plane The angle 540 A 540 = 79 
58' The mineral occurs also in granular 
and fibrous masses Its cleavage is per- 
v g ;-^\ feet parallel to oo P 06 (100) and only a 
t a \ *, little less perfect parallel to oP(ooi) 

a Wollastonite is usually colorless or 

TV 11 4. * o white, but in some cases is grayish, yellow- 

FIG -200 Wollastonite Crys- -uj-ir i 

tal with bP t ooi (c), oo POO, lsh > reddlsh or brown It is transparent 

ioo (a), -Poo, ioi (), or translucent and has a white streak, Its 

+P 55 , ioi (/), -hJP PO , luster is glassy except on the cleavage face 

102 () and oopf, S4 o (h) where it is often pearly. Its hardness is 



ANHYDROUS METASILICATES 369 

4 5-5 and density 2 8-2 9, and its refractive indices for yellow light 
are a=i 621, |8==i 633, 7=1 636 

Befoic the blowpipe wollastonite fuses with difficulty to a white 
transparent glass Its fusing point vanes between 1240 and 1325, 
diminishing with increase in iron It dissolves in HC1, leaving a residue 
of gelatinous silica, and is attacked vigorously by strong solutions of 
NaOH When fused it recrystalhzes in hexagonal crystals (pseudo- 
wollastonite) 

The mineral is distinguished from other white silicates by its crys- 
tallization, its cleavage and its solubility m hydrochloric acid Its prin- 
cipal alteiation is into apophylhte (p 443) 

Syntheses Ciystals of wollastonite have been made by fusing SiCfe 
and CaFa, and by dissolving the hexagonal modification (made by fusing 
and cooling wollastonite) in molten calcium vanadate at 8oo-9oo. 

Occurrence Wollastonite is characteristically a product of meta- 
morpluc pioccsscs, both contact and regional It occurs in metamor- 
phosed dolomites, in the limestone inclusions in the lava of Vesuvius, 
etc , in many gneisses and in some eruptive rocks. It is found also 
abundantly in caltaicous slags 

Localities Crystals of wollastonite aie found in the phonolite of the 
Kaiberstuhl, ncai Fmburg, Bavaria; m a contact metamorphosed lime- 
stone neai Cxiklova, Ilungaiy, in the limestone bombs in the lava of 
Mt, Somma, Naples, Italy, and of Santorm, Greece, and m limestone 
at Dunn, N Y Granulu or fibrous masses occur also at Attleboro, 
Penn , at dilTeient points in Lewis, Essev and Warren Counties, N, 
Y , and at the Cliff Mine, Keweenaw Pt , Mich. 

Pectolite (HNaCa 2 (Si0 3 )3) 

Pectolite was formerly regarded as a partially weathered wollastonite 
Recent analyses, however, indicate that it may have a definite compo- 
sition which can be represented by the formula written above, as shown 
by the analyses quoted below The excess of water shown by most 
analyses is ascribed to the admixture of some weathered material, 

SiOs AlaOs MgO CaO NasO K 2 EM) Total 

I. 54 23 33 72 9 34 .. 2 71 KX> oo 

IL 45 32 34 oo 9 32 , 2 55 100 30 

III 53 94 71 i 43 32 21 8 57 ,47 4 09 100 82 

I Theoretical 

IT Niakornat, Greenland Contains also u per cent 
TTT Point Barrow, Alaska 



.370 DESCRIPTIVE MINERALOGY 

The mineral usually occurs in fibrous masses of acicular crystals 
elongated in the direction of the orthoaxis, but in a few cases in tabular 
forms flattened parallel to oo P oo (100). Its cleavage is distinct parallel 
to the same plane 

Pectohte when pure, or nearly pure, is colorless or white or gray, and 
transparent or translucent Its luster is pearly on cleavage surfaces 
and satiny on fracture surfaces Its hardness is about 4 5 and its den- 
sity 2 88. When broken in the dark, some specimens phosphoresce 
Its average refractive index for yellow light is i 61. 

Before the blowpipe the mineral fuses to a white enamel It yields 
water when heated in the closed tube and when treated with hot hydro- 
chloric acid it decomposes, leaving a residue of flocculent silica. 

The principal alteration product of pectohte is talc (p 401). 

Synthesis Small, fine needles of pectohte have been produced by 
heating to 400 mixtures of Si02, AkOs, Na20, CaO and BfeO, in various 
proportions 

Occurrence. The mineral occurs in druses and as isolated crystals on 
the walls of cracks m eruptive rocks, and also in a few instances as vein 
fillings, and as a constituent of metamorphic rocks. It is mainly a 
secondary mineral 

Localities Crystals are found in seams m basalts at Edmburghshire, 
Scotland, at Bergen Hill, N J , in clefts in traprock, and in the eleohte- 
syemte at Magnet Cove, Ark (manganopectohte with about 4 per cent 
MnO) At Barrow Point, Alaska, fine-grained fibrous aggregates are 
found in abandoned workshops of the Eskimo Radially fibrous masses 
occur in the Thunder Bay region, Lake Superior, at Dibco, Greenland, 
and at a number of points in the Alps. 

Magnesmm-Calcium-Iron Pyroxenes 
Diopside-Augite 

The calcium-magnesium-iron pyroxenes include a number of com- 
pounds that have been given distinctive names They are apparently 
isomorphous mixtures of the metasihcates of Mg, Ca, Fe and Mn, or of 
these together with the magnesium and iron salts of the basic orthosilicate 
of iron and aluminium (Mg-Fe)((Al- Fe)0) 2 Si04. 

The crystals of all members of the group are alike in habit and similar 
m their mterfacial angles Their axial ratios are nearly the same and 
the angle ft has nearly the same value in all It is possible that the 
slight differences observed are due to the effect of the varying amounts of 
iron present. The crystals are nearly all short columnar in habit, with 



ANHYDROUS METASILICATES 



371 



the vertical zone well developed The simplest crystals are bounded by 
ooPob(ioo), ooP(no), ooPSb(oio) and P(Tii), but P(III), 
2P(22i), oP(ooi) and 2P 02(021) are also common (Fig 201) Other 
forms to the number of 95 have been observed, but they are compara- 
tively rare Contact and interpenctration twins are fairly common 
In the contact twins the usual twinning plane is oo P 66 (100) (Fig 202) 
Polysynthetic twins are twinned parallel to oP(ooi) In the mterpene- 
tration twins POO(IOI) (Fig 203) and Fa (Is 2) are the twinning 
planes The cleavage is parallel to oo P(iro), the cleavage angles being 
about 93 and 87* Partings are also common, parallel to one or the 
other of the three pinacoids 

All the pyroxenes of this group have a glassy luster and are trans- 
parent or translucent, Their color varies with composition as does also 



A 







FIG 201 



FIG 202. 



FIG 203 
FIG 201 Axigilc Crystal with oo P, no (m), oo P 55 , joo (a), oo P So , oio (b) and 

P, Tn(s), 

FIG 202, Augitc Twinned about oo P 65 (100) 
FIG 203 Interpenetration Twin of Augitc, with -P So (101) the Twinning Plane 

their hardness and density. The limits of hardness are 5 and 6 and of 
density 3 2 and 3 6. The streak of all varieties 'is white Pleochroism 
has been observed in some occurrences but it is not as noticeable as in 
the corresponding amphiboles. In the pyroxenes of this group it is 
usually in shades of green, but in the diallage of the Lake Superior region 
it is fairly strong in shades of amethyst 

Before the blowpipe the members of the group are fusible, their 
fusibility increasing with the quantity of iron present The fusing 
temperature of the pure diopside is 1381 and of hedenbergite xioo- 
1 1 60, The fusing points of the other pyroxenes of the group he between 
these temperatures None of the varieties are attacked by acids to any 
appreciable degree 

All the pyroxenes are distinguished from other minerals by their 
crystallization and their cleavage. 



372 



DESCRIPTIVE MINERALOGY 



Diopside is a mixture of the magnesium and calcium silicates m which 
the two molecules are in the ratio i i With the addition of the cor- 
responding iron molecule diopside grades into sahlite The calculated 
composition of a mixture of the formula MgCa(SiOs)2 is indicated in 
the first line The compositions of several typical diopsides are quoted 
in the following two lines 



Theoretical 
Albrechtsberg, Aus 
Alathal, Switzerland 



Si0 2 A1 2 3 Fe 2 3 FeO MgO CaO Total 

55 55 18 52 25 93 100 oo 

55 6o l6 5 6 18 34 26 77 101 43 

54 28 51 98 i 91 17 30 25 04 100 02 





Its crystals are usually characterized by the presence of the basal 

plane (Fig 204) The value 
of the angle no A 110=92 
So' 

Diopside is usually light 
green or colorless, yellowish, 
dark green or nearly black 
and rarely deep blue The 
lighter varieties are transpar- 
ent or translucent, the darker 
ones opaque The density of 
the pure mineral is 3 25. Its 
refractive indices for yellow 
light are. a 1.6685,18= 1.6755, 
7=16980, All these values 
increase with increase in the iron molecule Among the varieties that 
have been given distinct names may be mentioned 
Malacohte, a pale colored translucent variety, and 
Chrome^opstde, a bright green variety containing from one to 
several per cent CtaOs 

Diopside occurs in igneous rocks and in metamorphosed limestones. 

Hedenbergite is the calcium-iron pyroxene, though it always con- 
tains some of the diopside molecule The calculated compositions of the 
type mineral (FeCaS20e) and of a specimen from its best known locality 



FIG 204 Diopside Crystals with oop, uo 
(m), oo Poo, 100 (a), oopSb, O io (6), oP 
ooi (c), -P, in (), +2P, 221 (o), 3P3, 
31 1 (A), +P5o,Toi (p) 



are. 



Theoretical 
Tunaberg, Sweden 



Si02 AkOa FegOs FeO 

48 39 29 43 

47 62 i 88 10 26 29 



MgO CaO Total 

22 l8 IOO 00 

2,76 21. S3 lao 18 



ANHYDROUS METASILICATES 



373 




The mineral is black, except varieties that contain Mn which are 
grayish green It occurs in crystals (Fig 205) 
and m lamellar masses Its density is 3 31, and 
refractive indices for yellow light, a= i 7320, 
/3=i 7366, 7 = 1 7506 

m 

Sahhte. Intel mediate between diopside and 
hedenbergite are several pyroxenes which are 
characterized by possessing all three of the 
elements Ca, Mg and Fe in notable amounts 
Of these the most common is sahhte, which is FIG 205 Hedenbergite 
grayish, grayish green or black It occurs m Crystal Forms a, 
crystals and granular masses 

A typical analysis follows, the specimen 

, tr , , J A 

coming from Valpelema, Italy 



^ r ' > &> u an( * s as 
in F '? *4 Also aP * 

021 (s) and 



Si0 2 

54 02 



20 



FeO 

8 07 



MgO 

13 52 



CaO 

24 88 



Total 
100 69 



Schefiferite is a brown or black pyroxene characterized by the fact 
that it contains considerable manganese It may be regarded as heden- 
bergite m which a portion of the iron molecule has been replaced by the 
corresponding manganese molecule A specimen from the best known 
locality for the species Langban, Sweden gave* 



28, 



17, CaO=i9 62=99 22 



It occurs m tabular crystals that aie usually elongated m the direction 
of the zone ooPob (oio), P(Tn), Poo (Tor) and in crystalline masses 

The mineral is yellowish brown or black, according to the percentage 
of iron present Its sp gr. is 3.46-3,55 and its fusing temperature 

I200-I250 

A fine blue variety, known as wolan, from St Marcel, Italy, is char- 
acterized by the presence of about 5 per cent NagO, due possibly to the 
admixture of NaMn(SiOa)2 Its sp gr.=3 21. 

Jeffersonite is a variety containing zinc, occurring at Franklin Fur- 
nace, N J. It is found in large crystals with rounded edges Its color 
is greenish black on fresh fractures and chocolate brown on exposed sur- 
faces. An analysis yielded 

Si0 2 AlaOs FeO MnO ZnO MgO CaO H 2 Total 
49 91 i Q3 ro 53 7 oo 4 39 8 18 15 48 i 20 9862 



374 DESCRIPTIVE MINERALOGY 

Augite is the name given to the Ca-Mg-Fe pyroxenes containing 
alumina They are isomorphous mixtures of (Ca, Mg, Fe) SiOa with 
the alumino and ferric orthosilicates of the same metals, and often with a 
small quantity of the acmite or jadeite molecule The varieties of augite 
are numerous, their composition and properties differing with the pro- 
portions of the various molecules in the compounds The three most 
prominent varieties are 

Fassatie, a pale to dark green richly magnesian variety Sp gr = 
298 

Ordinary augite > a dark green or brownish black vanety, common 
in igneous rocks Specific gravity 3 24 For yellow light, a=i 712, 
5=1717,7=1733 

Diallage, a variety that is characterized by the possession of a 
distinct parting and a lamellar structure, usually parallel to oo P 60 
(100). 

Omphacite is a bright green sodic variety Sp gr =3 33 Analyses 
of fassaite (I), of three varieties of augite (II, III, IV) and of onipha- 
cite (V) follow. 

Si0 2 A1 2 3 Fe 2 0a FeO MgO CaO Na 2 Loss Total 

I 41 97 10 63 7 36 55 26 60 10 29 2 70 100 10 

II 50 41 6 07 i 09 6 78 12 92 22 75 100 02 

III 51 01 4 84 3 51 3 16 16 58 20 80 99 90 

IV 46 95 9 75 4 47 4 9 * 6 4 19 02 . 100 32 
V 54 21 10 91 3 12 i 33 10 03 14 61 4.51 .05 100 15 

I Grass green, Fassathal, Tyrol 
II Yellow, Monte Somma, Italy 

III Dark green, Monte Somma, Italy 

IV Black, Monte Somma, Italy 

V Omphacite from the Eclogite of Otztal, Tyrol Also 92% K a O and .46% TiO 8 . 

The augites are usually in short prismatic crystals (Figs. 201, 202). 
They are common constituents of igneous rocks 

All the pyroxenes of this group are subject to change under the 
conditions on the earth's surface Under the influence of the weather 
they alter to chlorite Under metamorphosing conditions they change 
into the corresponding amphiboles, more particularly into the bright 
green variety known as urahte. Alteration to serpentine is also 
common. Steatite, tremohte, epidote and other minerals are also 
frequent alteration products 



ANHYDROUS METASILICATES 375 

Syntheses Diopside and augite are common m furnace slags. They 
have been made by fusing their constituents m open crucibles, with or 
without the addition of a flux Molten hornblende crystallizes as 
monoclmic pyroxene 

Occurrence The most common methods of occurrence of the various 
pyroxenes have already been mentioned The magnesium-calcium 
varieties such as diopside and sahlite are found principally in metamor- 
phic limestones The green varieties are most common in schists and the 
black varieties m igneous rocks, especially the basic ones Augite often 
occurs also in ore veins, especially with magnetite 

Localities The occurrences of the various pyroxenes are so numerous 
that they cannot be enumerated here It will be sufficient to state that 
good crystals of diopside are found m the Ala Valley, Piedmont, at Zer- 
matt, in Switzerland, at Pargas, in Finland, and Nordmark, m Sweden. 
Hedenbergite occurs at Tunaberg, Sweden, and Arendal, Norway, 
scheffente at Langban, Sweden, and augite at Mt Monzom, m the 
Fassathal, Traversella, Piedmont; Mt Vesuvius, Italy, the Sandwich 
Islands and the Azores 

In the United States good crystals are found at Raymond and Rum- 
ford, Me (diopside, sahhte), at Edenville and Dekalb, N Y (diopside), 
and at Franklin Furnace, N J (hcdenbergite and jeffersomte) 

Alkali Pyroxenes 

The alkali pyroxenes are characterized by the piesence m them of 
alkalis, especially sodium They may be regarded as isomorphous mix- 
tures of the sodium, lithium, iron and aluminium metasihcates, thus 
Na2Si03+Fe2(Si0 3 )3~2NaFe(SiO;j)2, or NasSiQs+AhKSiOsJs-aNaAl 
($103)2 The three most common alkali pyroxenes are acmite, jaderie 
and spodumene Spodumene is used as a source of lithium Jadeite 
was formerly a favorite material from which to carve sacred emblems 

Acmite Aegirine 

Acmite has a composition corresponding to the formula NaFe(SiOa)2, 
and is rare More commonly this molecule is mixed with the augite 
molecule in the compound known as aegmne or aegmte, or aegmne- 
augite) according to the proportion of the augite molecule present 
When the mixture contains about 2,50 per cent Na20 the correspond- 
ing mineral is usually known as aegerine-augite. When MgO and CaO 
are absent (NagO 5 * 12-13 per cent), it is known as acmite. Between 
these limits it is aegirine. 

The calculated compositions of the pure acmite molecule and the 



376 



DESCRIPTIVE MINERALOGY 



composition of specimens of acmite, aegirme and aegirme-augite as 
found by analyses are 



Sl02 

I Si 97 

II. 51 66 

III 49 3 2 



A1 2 3 Fe 2 3 
34 60 
28 28 

4 88 16 28 



IV. 5 33 30 



FeO MgO CaO 

5 23 

5 65 4 28 9 39 

12 37 10 98 22 01 



Na 2 

13 43 

12 46 

8 68 
2 14 



K 2 

43 
68 

94 



Total 

100 OO 

too 25* 

ioo 41 t 

99 73 J 




I Theoretical acmite 
II Acmite, Rundemyr, Norway 

III Aegirme, Sarna, Dalekarhen 

IV Aegirme-augite, Laurvik, Norway 

* Contains also 69 per cent MnO, 39 per cent H 2 and i 11 per cent TiOj 
t Contains also i 25 per cent TiOa 
t Contains also 66 per cent TiQj 

Acmite crystals are usually more acicular m habit than those of the 
ordinary pyroxenes, and their terminations are steeper P(Tn) and 
Poo(Toi) are common and 6P("66i) and other 
steep pyramids are not uncommon (Fig 206). 

The mineral has a vitreous luster, and is 
transparent or translucent Its color is reddish 
brown to brownish black and In some cases 
green Its hardness is 6 and sp gr. = 3 52 Its 
refractive indices for yellow light arc. a = 1,7630, 
j3=i 7990, 7=1 8126 

Aegirme is greenish black Its streak is 
yellowish gray or dark green. Plcochroism is 
strong in green and brown tints. Haulncss is 6 
and density 3 52 

Before the blowpipe acmite and aegirine fuse 
to a black magnetic globule The fusing tem- 
perature of acmite is from 970 to 1020 Both 
minerals are slightly attacked by ucul before and 
after fusing 

Synthesis Acmite has been made by the 

fusion of a mixture of powdered quartz, FfyQz and NiioCO;* in the pro- 
portions indicated by the formula NaFe(SiOs)2 

Occurrence Both minerals are limited m their occurrence to soda- 
nch igneous rocks, in which they are primary 

Localities Crystals of acmite occur in a dike of pegmatite near 
Eker, Norway, and in a nephelme syenite at Ditro, Hungary. 



FIG 206 Acmite Crys- 
tal with oo p 60 , ioo 
(a), oo Poo, oio (6), 
_oop, no (m), +P, 
in (5), +3P5> 3" 
(5), +6P, 56t (0) 
and 8P, SSi (12) 
and Q merge 



ANHYDROUS METASILICATES 377 

Aeginne crystals are more common They occur abundantly in the 
nephehne syenite dikes in the neighborhood of Langesundf jord, Norway, 
m some instances in crystals a foot long. They are found also in can- 
cnmte syenites at Elfdalen and elsewhere in Sweden, in nephehne 
syenite on the Kola Peninsula, Russia, and in the same rock at Hot 
Springs, Ark. 

Jadeite (NaAl(Si0 3 ) 2 ) 

Jadeite is not known in measurable crystals, but, because sodium 
is almost universally present in the mineral spodumene, where it is ap- 
parently in isomorphous mixture with LiAl(Si03)2, it is assumed that the 
molecule NciAl(Si03)2 ciystalhzes in the same way as the spodumene and 
the acnnte molecules Most specimens of jadeite are isomorphous mix- 
tures of the jadeite and diopside molecules When in addition to these 
there is a notable admixture of the acmite molecule, NaFe(SiO,3)2 7 
the mineral is known as chloromdamte 

The mineral is of great ethnological interest because so many orna- 
ments were made of a rock composed mainly of jadeite by the ancient 
inhabitants of China, Mexico, South Amenca and elsewhere " Jade " 
ornaments, however, arc not all made of jadeite, but m all instances their 
material resembles this mineral in color, structure and density Many 
of them aie made of fibrous aniphiboles, some of which correspond to 
jadeite in composition 

The theoietical composition of the mineral is given in line I, and the 
analyses of specimens from Mexico and China in lines II and III, 



AbO,i FcO MgO CaO NagO KgO H 2 Total 

I 59 39 25 56 IS 35 ioo oo 

II 58 18 23 S3 i 67 1,72 2 35 n 81 77 53 100 56 

III. 58 68 21 56 94 2 49 3 37 13 09 49 . . 100 62 

I Theoretical 
II Oavua, Mexico 
III Ornament, China 

Jadeite occurs in fibrous, flaky and dense, finely granular masses 
with a glassy luster, inclining to pearly on cleavage surfaces Its color 
is in some cases white or yellowish white, but more frequently bright 
green or bluish green. Its streak is white Its cleavages make angles 
of 87 Its fracture is tough and splintery. Its hardness is 6 7 and its 
density 3.3-3 35. Its intermediate index of refraction, =* 1.654 

Before the blowpipe jadeite fuses easily lo a transparent, blebby glass 
It is unattacked by acids. After fusion, however, it is easily decomposed 



378 DESCRIPTIVE MINERALOGY 

by HC1 and sometimes by Na 2 C0 3 At high temperatures (225 
235) it is also decomposed by water 

Jadeite alters by metamorphic processes to a white hornblende 
(tremohte) 

Localities Ornaments and instruments made of jadeite, and water- 
worn fragments of the mineral are known from many localities in China, 
Tibet, Burma, Switzerland, France, Egypt, Italy, Mexico and Central 
America The original sources of the material of the ornaments are 
not known The mineral, however, occurs with albite and nephelme 
in a dike at Tawman, Burma, and probably as a constituent in some 
metamorphic schists. 

Spodumene (LiAl(Si0 3 )2) 

Spodumene is essentially the lithium molecule corresponding to the 
sodium molecule jadeite Nearly always, however, the mineral contains 
some of the sodium molecule, and a small quantity of helium Three 
typical analyses are quoted below 

Colorless, Yellowish green, Kun*lto, 

Theoretical Branchville, Mmas Geraes, S Diego 

Conn Brazil Co , C tl 

Si02 64 49 64 25 64 32 64 42 

27 44 27 20 27 79 27 32 

20 



FeO 67 

CaO 17 

Li20 8 07 7 62 74? 7 20 

Na 2 39 55 39 

K 2 . 03 

24 12 



Total 100 oo 99 90 101 07 99 51 

Crystals are usually columnar parallel to oo P (no) or tubular par- 
allel to oo P 66 (100) (Fig 207) They are more complex than those of 
the members of the diopside-augite group and their habit is different 
The most frequent forms are ooP 60(100), ooPob(oio), coP(ixo), 
ooP2(i2o), ooP3(i 3 o), 2PSb(o2i), 2P(22i) and P(Tn) Some of 
them are of enormous size In the Etta Mine, Black Hills, South 
Dakota, are many 30 ft long and 3-4 ft. in diameter. One meas- 
ured 47 ft, in length. Most crystals are striated vertically. Twins are 



ANHYDROUS METASILICATES 379 

fairly common, with ooP(no), the twinning plane Although ciystals 
are not uncommon the mineral more fiequently occurs as platy or scaly 
aggregates The angle no A ilo=93 

Spodumene has a glassy lustei, which is pearly on cleavage surfaces 
Its color is white, gray, greenish or yellowish 
green, or amethystine It is transparent or 
translucent, and its streak is white Its 
fracture is uneven or conchoidal, its hardness 
between 6 and 7 and its density 3 2 Dark 
green crystals exhibit marked pleochroism 
Refractive indices for yellow light in speci- 
mens from North Carolina are a=i65i, 
18=1669, 7=1677 

Two varieties have been named and used 
as gems These are FlG 2 7 Spodumene Crys- 

OAMfe, a glassy emerald-green variety, ^^ ~ gj 
from Alexander Co , N C W| ^ I20 ' (ju) , P ^ 

Kut^s^te, a pmk or lilac variety, from 130 (), 2? So, 021 (d), 
San Diego Co , California Under the mflu- -HP, 221^ (r), +P, m 
ence of radium rays it becomes green When M > 2P 2 , 2 1 1 (/) and P 65 , 




IOJ 



heated to 240 it becomes a darker rose 
color, but at 400 it loses all color 

Before the blowpipe the mineral swells up and fuses to a colorless 
glass, at the same time imparting a crimson color to the flame It is 
unat tacked by acids. It melts at about 1325 Its powder reacts 
alkaline 

It alters readily to albite, muscovite, eucrypfate (LiAlSiOt), or mix- 
tures of these One of the commonest mixtures is known as cymatchte 
or cumatohte. The mixture of albite and eucryptite has been called 
$ spodumenc, 

Spodumene crystals have not been made artificially 

Occurrence atid Origin The mineral occurs in granites, pegmatites 
and ciyRtallme schists, where it was formed by pneumatolytic processes 
It is often associated with cassitente 

Localities Spodumene crystals occur at Huntmgton, Mass , in a 
quartz vein m mica schist, at Branchville, Conn ? in pegmatite, at 
Stony Point in Alexander Co , N. C , in cavities m a gneiss, at the Etta 
Mine and at other places in the Black Hills, N D,, in a pegmatite; at 
the lepidolite localities in California and in Mmas Geraes, m Brazil 

Uses The ordinary varieties of the mineral are used as a source of 
lithium m the manufacture of lithium salts, and the transparent varieties 



380 



DESCRIPTIVE MINERALOGY 



as gems The total production of kunzilc m this country during 1912 
was valued at $18,000, all from California One specimen found in this 
year weighed 47! oz Another was a crystal measunner 9X5X7 inches 
The other forms of the mineial were not mined In teccnt years a few 
tons have been furnished by the mines in the Black Hills 

TRICL1NIC PYROXENES 

The trichmc pyroxenes include the four mmcials rhodonite, bmtamtlc, 
fowlente and babingtonite They are completely ibomoiphous The 
first is the manganese metasihcate, MnSiOs, and the otheis aic iso- 
morphous mixtures of this molecule with the con expending silicate of 
calcium (bustarmte), or of these two with the corresponding 11011 (babmg- 
tornte), or with the iron and zinc compounds (fowlente) 

RhodomteFowlente (R"MnSiOa. R = Ca,Fe,Zn) 

Rhodonite is the pure manganese silicate with the pcitentagc com- 
position shown in I In II is the result of an analysis of ciyslals fiom 
Pajsberg, Sweden An analysis of bustamite fiom Campiglia, Italy, is 
quoted in III and one of fowlente from Franklin Funute, N J., in IV 

Si0 2 A1 2 3 MnO FeO ZnO M0 CaO H a O Total 



I 458s 

II 45 86 

III 49 23 

IV 46 06 



37 



54 IS 
45 92 
26 99 



36 

i 72 



i 65 
i 81 



34 28 3 63 7 33 



40 

18 72 

7 04 



JOO OO 

100 09 

100 38 

<><; 04 



All are trichmc (pmacoidal class), with the aual constants of 

10729 : T : .6213, =-io3 

lO'.jS-ToB^'.r-Si JO' 

for rhodonite, and i 0807 : i 
: .6237 and 01-102 27', 
jS=io834 / , 7-82 S3 X for 
bahmgtonitc. Thoir crys- 
tals possess many habits, of 
which the cubical, tabular, 
and columnar arc the most 
Fig 208 Rhodonite Crystals with 'p, i7o common. They an k usually 

(JO* P'' 110 (), oP, ooi (<;), oo pas, rough with rounded edges, 

ioo (a) I,-" Poo ,010(6), 2,P, 221 Wand 

221 (n) 





oo P 08(100), oo P 06(010), 



The most f requont i y 

f ' -' . 

curnng forms are oP(ooi), 
oo'PCiTo), P/(iu") and 



2,P(22i) (Fig 208) The angle ioo A 001*72 37', Their cleavage 



ANHYDROUS METASILICATES 381 

is perfect parallel to ooP'(no) and oo 'P(i To) Although crystals are 
fairly common in some places, the minerals are more usually in dense, 
structureless or finely granular masses 

All the trichnic pyroxenes have a glassy luster which is somewhat 
pearly on cleavage surfaces They are transparent or translucent and 
all except babmgtomte have a rose-red color when pure When mixed 
with other substances their color may be yellowish, greenish, brownish 
or black They are pleochroic in rose and yellowish tints Their streak 
is always reddish white Babmgtomte is greenish black and is pleo- 
chroic in green and brown tints All have an uneven fracture Dense 
varieties are tough and their crystals are brittle Their hardness 
= 5-6, and density 3 4-3 7 The intermediate refractive index of rhodo- 
nite is i 73 for yellow light 

Before the blowpipe all become black, swell and fuse to a brown 
glass The fusing tempeiature of rhodonite is about 1200 and of 
bustarmte about 1300 They are attacked by acids with loss of color 

When exposed to the weather the membeis of the group containing 
manganese alter to a mixture of which the principal constituents are a 
manganese OKide, M^Os, silica and water, or to mixtures of carbon- 
ates of manganese, or a mixture of the carbonates of manganese, iron 
and calcium 

Syntheses Crystals of rhodonite have been prepared by fusing a 
mixtuie of SiCfe and MnCte and bypassing a current of steam and COa 
over a icd-hot mixture of MnCb and Si02 Rhodonite and babmgton- 
ite crystals are also formed in the slags of manganese iron furnaces, and 
the latter has been found in cavities in roasted iron ores 

Occurrence The members of the group containing manganese occur 
m veins of magnetite, copper and other metals, and in contact zones 
between limestones, shales and igneous rocks, associated with other 
manganese minerals. Under these conditions they may have been pro- 
duced by the help of magmatic emanations Rhodonite occurs also with 
rhodochrositc in deposits of manganese ores and in other associations, 
where it may be of secondary origin. Babmgtomte occurs principally 
as a rare component of siliceous rocks 

Localities Crystals of rhodonite and bustamitc occur in iron ore 
deposits in the gneiss of Langban, Sweden Fine crystals of rhodonite 
are found m the iron ore at Pajsbcrg, Sweden, and crystals of fowlente 
in metamorphosed limestone associated with the zinc ores at Stirling 
Hill and Franklin Furnace, N J Massive rhodonite is abundant at 
Jekatermburg, Ural, Russia, at Kapmk, Hungary, at Blue Hill Bay, 
Maine, and in Jackson Co., N C, associated with wad Massive bus- 



382 DESCRIPTIVE MINERALOGY 

tamite occurs at Rezbanya, Hungary, in veins m limestone, and at Mts 
Civillma and Campigha, Italy, m fibrous masses Babingtomtc occurs 
in a mica schist at Athol, Mass , and m druses in granite at Baveno, 
Italy, and in the ore veins at Arendal, Norway 

The principal occurrences of gem rhodonite in this country are in 
Siskiyou Co , Cal , and near Butte, Mont In the former locality the 
mineral occurs nine miles north of Happy Camp m a fine-grained 
quartz schist It consists of a mixture of quartz grams cemented by 
rhodonite and traversed by veins of pyrolusite The Montana material 
is in radiating groups with quartz, pyrite and brown manganese ovide 
At the Alice Mine it is associated with rhodochrosite 

Uses and Production Transparent rhodonite is used as a gem-stone 
to a slight extent The total yield of the material m the United States 
during 1912 was valued at $550, 

THE AMPHIBOLES 
(R"Si0 3 , R'At(Si0 3 ) 2 and R"(R"'0),Si0 4 ) 

The amphiboles are common alteration products of pyroxenes and 
some other silicates The> are also abundant as components of ceitain 
schistose rocks, as for instance, the hornblende schists, and they otuu 
also as original constituents of igneous rocks. The crystals of till the 
amphiboles are similar m habit to those of the pyroxenes (Fig 209), 
but since the ratio between the a and b axes is about > to i , the angles 
between their cleavage planes, which, like those of the pyroxenes, are 
parallel to ooP(no), are from 54 to 156 and 124 to 126 (see Fig 
igSB) The plane of symmetry bisects the obtuse angle. 

The members of the group are about as numerous (is those of the 
pyroxenes, but the common types are much fewer. Moreover, there is 
no subgroup corresponding to the wollastomte subgroup of the pyrox- 
enes. The best known members of the series, with their axial Mtios *ire: 

Orthorhombit (possibly twinned monoclhuc) 

Anthophylhte f (Mg Fe)SA 1 fl fc - r* 521 : i * a-fe 

Gcdnte { (Mg.Fe)(A10) 2 &iO 4 } -.523 i . .^17 

Monochmc (monochmt prismatic class), 

Tremolite Mg s Ca(Si0 8 ) 4 a 6 : r,s4T5 ' r * .3886 

Actouhte (Mg Fe) 8 Ca(Si0 3 ) 4 

Cummingtonite (Fe MgJSiOj 
Gr&nente FeSi0 8 

" (Mg Fe),Ca(Si0 8 )< 



Hornblende 



(Mg Fe)((Al 
NaAl(Si0 8 ) 3 



.2937 



ANHYDROUS METASILICATES 383 

}NaAl(Si0 3 ) 2 1 
Glaucophane { (Fe Mg)SlOl } * S3 i 29 /3- 7 7 

[ (Na 2 Ca Fe)Si0 3 ] 

Arfvedsowte | (Ca Mg)((Al Fe)0) 2 SiO' J " S4 9 6 r 2 75 = 7545' 

Riebeckilc NaFe(SiO,)2 =5475 i 2925 = 76lo' 

| NaFe(SiOJ 1 
Crocidohte j j^o ] 

Tnclmic (tnclmic pinacoidal class) 
Aemgmatite Na 4 Fei)(Al Fe)^(Si TiJi^O* = 6778 i 3506 j8 = 7249' 

ORTHORHOMBIC AMPHIBOLES 

Anthophyllite Gedrite 

The orthorhombic amphiboles are comparatively rare They are 
isomorphous mixtures of MgSiOa, FeSiOs and the alummo-orthosihcates 
(Mg- Fe)(A]0)oSi04 The pure MgSiOa has not been found in nature, 
but it has been produced in the laboratory The mixture of the mag- 
nesium and iron silicates (Mg-Fe)Si03, is known as anthopkylhte. In 
nature it always contains a little of the molecule (Mg-Fe)(A10)sSiOi 
Gedrite, which is much less common than anthophyllite, contains more 
AbOs than does this mineial, which may be regarded as due to a larger 
admivtuic of the molecule (Mg Fe)(A10)2SiOi. The name is thus 
applied to aluminous anthophylhtcs 

The difference in composition of the two minerals is shown by the 
following analybct. of (I) anthophylhte and (II) gednte 



Si0 2 FeiAi AbO,j MnO FeO MgO CaO Na 2 H 2 Total 

I 57 98 63 31 10 39 28 69 20 i 79 99 99 

II 46 18 44 21 78 .. 2 77 25 05 . 2 30 i 37 99 89 

I Brown crystals, Franklin, Macon Co , N C- 
II Colorless prisms, Fibkcrnas, Greenland 

The orthorhombic amphiboles usually occur in platy or fibrous 
aggregates that rarely show traces of end faces, and, consequently the 
ratio between c and b is not accurately known. The planes in the pris- 
matic zone are, however, sometimes so well developed that they 
can be recognized as oopco(ioo), ooP 06(010), and ooP(no) 
Cleavage is perfect parallel to oo P(xio) and distinct parallel to oo P 36 
(oio) The cleavages intersect at angles 54 2o'-55 i8\ 

The minerals have a glassy luster which is slightly pearly on cleavage 
surfaces They are green or brown in color and have a colorless, yellow 
white or gray streak and are translucent and pleochroic in colorless, 



384 



DESCRIPTIVE MINERALOGY 



greenish and brownish tints Their fracture is somewhat conchoidal 
Hardness is 5 5 and density 3 2 The refractive indices for yellow light 
m anthophyllite are ^=1633, 18=1642, 7=1 <>57, and in gednte, 
i 623, i 636, and i 644 

Synthesis Pure magnesium metasihcate has been made in ortho- 
rhombic crystals mixed with monochmc crystals, by rapid cooling of a 
magma made by heating Mg salts and silica with water at 375-47s 

Occurrence The minerals are found in crystalline schists more 
particularly in hornblende gneisses and hornblende schists, where they 
are distinctly metamorphic minerals, having been derived in some cases, 
at least, by the alteration of the orthorhombic pyroxenes They alter 
to talc 

Localities Anthophyllite occurs in dark brown platy abrogates at 
Kongsberg and Modum in Norway, associated with hornblende in mica 
schists, on the Shetland Islands, Scotland, associated with sei pen tine, 
and at the Jenks Corundum Mine in Macon Co , N C 

Gednte occurs in yellowish gray fibrous aggregates at Bamlc, Norway, 
in dark brown aggregates associated with magnetite and brown mica, at 
Gedres, Hautes-Pyr&iees, France, and m a mica schist at Fiskernas, 
Greenland, associated with a large number of metamorphic minerals 

MONOCLINIC A.A1PHIBOL&S 

The monochmc amphiboles, like the corresponding pyroxenes, com- 
prise isomorphous mixtures of the metasihcatcs of No,, Mg, Ca and Fe 




\ 




m 


a 


m 


* 


\ 






j/ 


X 




^ 





/ 

5 



FIG 209 Ampibole Crystals with o P, no (m}, oo p Sb , oio (6), *> PJ, 130 (e); 
P w , on (r) and -P So , jor (/). 

and the basic orthosihcates of Al and Fe Recent work seems to indi- 
cate that in tremolite there is present also a little HkCX In the amphi- 
boles the alummo-silicate is more common than in the pyroxenes and 
consequently aluminous amphiboles are more common than aluminous 
pyroxenes 



ANHYDROUS METASILICATES 385 

All the monoclimc amphiboles crystallize with the same habit in 
crystals that are columnar like those of the corresponding pyroxenes, 
but on which the terminations are different (Fig 209) Moreover, all 
have a distinct cleavage parallel to oop(no) with cleavage angles of 
about 56-! 24 

The amphiboles aie distinguished from other minerals by their 
crystallization and their cleavage 

For convenience, the monoclimc amphiboles may be subdivided into 
(i) the magnesium-calcium-iron amphiboles including tremolite^ actino- 
hte, cummmglomte, gtunente and hornblende, and (2) the alkali amphi- 
boles, including aifvedsomte, glaucophane and nebecfote 

Before the blowpipe all the members of the group fuse to a glass which 
is coloiless, green or black, according to the quantity of iron present 
The varieties rich in iron are attacked by acids 

Magncsium-Calcium-Iron Amphiboles 
Tremohte-Hornblende 

This group includes the monoclimc amphiboles that are mainly meta- 
silicates of magnesium and iron and the mineral hornblende, which is a mix- 
ture of these molecules and the orthosihcate (Mg Fe)((Al'Fe)0)2Si04 
The calcium mctasihcate is present in some members as an isomorphous 
mixture, but it does not occur alone as an independent member corre- 
sponding to wollastomtc among the pyroxenes Hornblende is the only 
member of the series that is essentially aluminous 

The ciystals of the monoclimc amphiboles are short columnar or 
long and acicular. Their axial ratios are nearly alike and their cleavage 
angles differ only by a few minutes. The simplei crystals are bounded 
by ooPob(ioo), oo P 03(010), ooP(no), oP(ooi), 3? 00(031), 
+P6o(Toi), -Pob(iot), 2P2(T2i), 2PI(2ii) and POO(OII) (Fig 
209). Contact twins arc common, with cop<x>(ioo) the twinning 
plane as m the pyroxenes Polysynthetic twins are larc 

All the amphiboles of this group have a glassy luster and are trans- 
parent or translucent All the members but hornblende arc white or 
some shade of green, though colorless and brown varieties are not un- 
common and yellow and red varieties are known. Hornblende is fre- 
quently so dark as to be almost black Their streak is light, hardness is 
5-6 and density 2 0-3 4> depending upon composition 

The cleavage is perfect in all the amphiboles and there is present 
often also a parting parallel to oo P oo (too) and P oo (Toi), the latter due 
to gliding Pleochroism is strong m all the colored varieties m green 



386 DESCRIPTIVE MINERALOGY 

and yellowish green tones in the green varieties, and brown and yellow- 
ish brown tints in the brown varieties 

Tremolite is the calcium magnesium silicate When there is mixed 
with this the corresponding iron molecule the mixture is known as 
actinohte if the proportion of the iron molecules present is not great 
The theoretical compositions of the two molecules Mg3Ca(Si03)4 and 
Fe 3 Ca(Si03)4 are given in lines I and II, and analyses of several trem- 
olites and actmolites in lines III, IV, V and VI The almost universal 
presence of small quantities of water m trcmohtc, and the Lick of 
enough Mg, Ca, Fe and other metallic bases to satisfy all the SiOj re- 
vealed by the analyses has suggested to some muicialogLsts that the 
water is an essential part of the compound, and that its composition is 
best represented by 



Si0 2 A1 2 3 Fe 2 3 FeO MgO QiO Na 2 O HoQ Total 

I 57 72 28 83 13 4 1 ) ioo oo 

II 46 90 42 17 10 93 ioo oo 

III 58 27 33 tr 25 93 ii 90 T 25 i 22 09 40* 

IV 57 40 38 i 3 6 2 S 6 9 *3 89 40 99 12 
V 58 80 3 05 22 23 16 47 TOO 55 

VI 55 50 6 25 22 56 13 46 A 29 99 06 

I Theoretical for MgsCa (SiO.)* 

II Theoretical for Fc,Ca (SiOi) 4 

III Tremohte, Easton, Pa 

IV Tremolite, Gouverneur, N Y 
V Asbestus, Bolton, Mass 

VI Actmohte, Gremer, ZillerLhal, Tyrol 

*Also oSMnOand 42 



Tremolite is white 01 nearly white, and actinolite is green The 
former occurs in columnar crystals, in plates and occasionally in libers, 
while actinolite is nearly always in long, slender acicular ciystals without 
terminations The refractive indices for yellow light in tiemoliteiue 
ct-i 6065, j8=i 6233, 7=1,6340. In actmohie, j~i,6n(), 0=-i 6270, 
7=16387 

Both minerals melt in the blowpipe flame, the fusing temperature 
for tremohte being about 1290 and for actinolite about 1150. 

Asbestus is a fibrous variety of tremolite, actinolite or anthophylhto. 
It occurs principally in rocks that have been crushed and wheaml under 
great pressure The actinolite asbestus is used for the same purpose as 
the chrysotile variety (see p 398), but it is regarded as less valuable. 



ANHYDROUS METASILICATES 387 

Its principal source in this country is Sails Mountain, Georgia, but prom- 
ising deposits have recently been reported near Kamiah, Idaho At the 
Georgian locality the asbestus forms distinct lenses in gneiss It is 
possibly an altered basic intrusive rock, 

Smaragdite is a grass-gieen actmohte, which is often an alteration 
product of pyroxenes and ohvine The name is also applied to a bright 
green hornblende containing a little chromium 

Nephrite is a finely fibrous actmohte or tremohte and usually some 
chlorite, forming dense rock masses that are white or of a light green 
coloi It was formerly much ubed, like jddc, in the manufacture of 
images, charms and implements 

Cummingtonite a,nd grimerite aic amphiboles containing notable 
quantities of the molecule FcSiO* In grunente, the qudntity of Mg 
present is very small but in cummmgtomte it is fairly large Because 
of its similarity to anthophyllite, this mineral is frequently referred 
to as amphibole-anthophylhtc It is intermediate in composition 
between grunente and actmohte Analyses of specimens from several 
well known localities are quoted below 



SiOa Al 2 Ch FcaOs FeO MgO C<iO Na 2 H 2 Total 
I 57 26 75 i 73 15 64 21 70 tr 2 80 99 88 

II 47 17 i oo i 12 43 40 2 61 i 90 47 2 22 100 08 

I Cummingtonite, near Baltimore, Mel 

II Grunente, CollobriSres, France Contains also, F 07, KaO^ 07 and 
MnO~ 08 

These two minerals are comparatively rare and have not always 
been recognized as worthy of different names In general appearance 
they are much like actinohte, though perhaps more brown or gray in 
color, and they occur in nearly the same association The specific grav- 
ity of cummmgtonite varies between 3 i and 3 3 and that of grunente is 
about 3 52. The intermediate refractive index for yellow light is i 62- 
1.65 in cummmgtonite and 1.697 in gninerite 

Hornblende is the name given to the monoclmic aluminous aznphi- 
boles that contain only a small quantity of alkalies. In other words, 
most of the hornblendes are isomorphous mixtures of the actinolite mole- 
cule and the molecules (Mg- Fe)((Al- Fe)0)aSi04 and (Na- K)Al(SiO)2 
The varieties containing NdaO (known as katojorrfc) correspond to 
aegirme among the pyroxenes 



388 DESCRIPTIVE MINERALOGY 

The varieties of hornblende that are distinguished by distinctive 
names are 

Pargasite, the green, bluish green or greenish black variety, and 

Edemte, the white, gray or light giccn variety, both of which con- 
tain very little iron m either the ferrous or feme condition, 

Smaragdite, a bright green chromiferous variety of parasite, 

Common hornbletide, the greenish black vanety, 

Basaltic hornblende, which contains a laige pioporlion of ferric iron 
and is black in color 

Their refractive indiceb for yellow light aic as follows 

ft 7 

Pargasite, Pargas, Finland i 613 i 020 r 632 

Common Hornblende, Kragero, Norway t 629 T 042 i 6153 

Basaltic hornblende, Bohemia i 680 i 725 t 752 

The fusing temperature of pargasitc is about 1150 and of horn- 
blende about 1200 

Analyses of typical specimens of these varieties follow 

Si0 2 A1 2 3 Fe 2 03 FeO MgO CaO Niii0 K a O Tn Total 

I 51 69 4 17 2 34 9 83 17 17 12 17 82 79 i i^ 100 25 

II 42 97 16 42 . i 32 20 14 14 90 i 53 2 85 87 102 75 

III 49 33 I2 7 2 * 7 2 4 63 17 44 9 Qi 2 25 03 *<) <)g 15 

IV. 39 17 14 37 12 42 5 86 10 52 n 18 2 48 2 OJL 39 99 91 

I Common Hornblende, Vosgcs Aho 14 per < cnl T\(\ 

II Pargasite, Pargas Finland Also i 66 per tent F 

III Edemte, Saualpen, Cannthia Also 1.21 per tent K 

IV Basaltic, Jan Maycn, Greenland Albo i 51 [>er <uul MtiO 

Among the commonest forms of alteration in lhi umphihoIoR 
are the following Tremolite into tile (p 401) and wipcntiiu*, and 
hornblende into serpentine, chlorite (p 428),q>idolu and Imitiie, often 
with the addition of magnetite and other iron compounds in oases where 
iron was present in the original mineral Most of these thungcs me 
brought about by regional metamorphism. The production of hiotiie is 
also brought about by the action of magmas The common weathering 
products of hornblende are chlonte, epidote, culcite, quarts, magnetite 
and sidente Under the conditions of high temperature and high pres- 
sure, hornblende sometimes passes over into augite and magnetite. 

Syntheses. Amphibole crystals have not been found in slags nor 
have they been made by dry fusion. Crystals of hornblende, however, 



ANHYDROUS METASILICATES 389 

have been obtained by heating to 555 for three months, a mixture of 
its components in a glass tube with water 

Occurrence Tremolite occurs m crystalline limestones and dolo- 
mites that have been subjected to regional metamorphism and in crys- 
talline schists Actmohte, cummmgtomte and grunente are found in 
crystalline schists, in some cases m such laige quantity as to constitute 
essential parts of the rocks Actmohte schists are such rocks containing 
in addition to the actmolitc some quartz, epidote and chlorite Gru- 
nente schists consist essentially of gmnente, actmohte, magnetite and 
quarts 

Common hornblende occuis m igneous and metamorphic rocks, 
such as gneisses and schists In some schists, as the amphibohtes, 
it is the puncipal constituent and m others, the hornblende schists, 
it is the principal component other than quartz The mineral is 
also a common metamoiphic alteration product of pyroxenes vhich 
it frequently pscudomorphs When the pscudomoqjhmg hornblende 
ib blue-green and fibrous it is known as urahte The chemical 
changes attending this alteration aic illustrated by the analyses of a 
pyio\ene (I) from the Grua Tunnel in Norway and of the urahte (II) 
produced from it 



AlaOs FcO MnO CaO MgO NagO Loss Total 
I 5 S3 * 9* 2 7 7 81 i 99 24 51 10 92 48 26 100 37* 
II 42 02 2 30 3 25 9 30 94 20 90 9 63 45 i 07 100 04* 

* Also 19 per cent Kj0 m I anJ 26 per cent in IE 

Basaltic hornblende is found only in igneous rocks, and especially 
those rich miion 

Edenite occurs in ciystalhnc limestones that have been metamor- 
phosed by contact action 

Pargasite is in gneisses and crystalline limestones 

Localities Tremolite crystals occui at Campolonga, Switzerland; 
at Rezbanya, Hungary, at New Canaan, Conn , and at Diana, Lewis 
Co , N. Y It occurs also in flat plates at Lee, Mass ; near Byram, 
N J ; at Easton, Penn , at Edenville, N Y., and at Litchfield, Me,, 
and other places in the limestones in Quebec, Canada 

Actmohte occurs with chlorite at the Zillerthal, Tyrol, in talc and 
chlorite schists near Jekatermburg, Ural, Russia; at Arendal, Norway, 
at Willis Mt , Buckingham Co., Va , at the Bare Hills, Md,; at Mineral 
Hill, in Delaware Co , and at Unionville, Penn , in the soapstone 
quarries at Wmdham and New Fane, Vt , at Bolton, Brome Co , 
Quebec, and at many other points. 



390 DESCRIPTIVE MINERALOGY 

Asbestus is abundant at Sterzig, in Tyrol, on the Island of Corsic 
near Greenwood Furnace, N Y , in the Bare Hills, neai Baltimore, JVL 
at Pylesville, Harford Co , in the same State, at Barnet's Mills, Fau 
quier Co , Va , and at the localities at which it has been mentioned as 
being mined 

The principal occurrences of cummmgtomte arc kongsbcig, Norway, 
Cummmgton, Mass, and a layer m gneisses and schists at Mt 
Washington, Md 

Grunente occurs in a rock composed of this mineral, gai net and hem- 
atite near Collobneres, Var , France It has also been dcbcribcxl as the 
principal constituent of certain schists in the Lake Supenoi iron icgion, 
but since the amphibole in these locks contains a notable quantity 
of MgO it should better be classed -with cumminglomle 

The localities at which crystals of the hornblendes have been 
found are very numerous. Excellent crystals occui in Ihc volcanic 
bombs in the Lake Laach district, Prussia, in cavities in inclusions 
within the lavas of Aranyer Mt , Siebenburgen, Hungary, m the dikes 
of porphyry, near Roda, Tyrol, on the walls of cavities m inclusions in 
the lavas at Vesuvius, Italy, and at various points in Sweden, etc In 
North America fine crystals are found at Thonu&ton, Me , at Russell 
and Pierrepont, N Y , at Franconia, N H , and in the glacial debris 
at Jan Mayen, Greenland. Pargasite occurs at Paigas, Finland, and 
Phippsburg, Me 

Alkali Amphiboles 

The alkaline amphiboles include mbeckite> croadohtc, glaucoplmue 
and arfvedsomte The first two are nonalummous iron-soda umphiboles 
and the last two are aluminous compounds Glaucophonc contains the 
molecule NaAl(Si03)s which is found also in hornblende, and, therefore, 
it may be regarded as a connecting link between the common and the 
alkaline amphiboles Glaucophane differs from hornblende, however, 
m containing very little CaO, The intermediate link halo/onto bridge* 
the gap between the two. 



Glaucophane is, theoretically, a mixture of the two molecules 
NaAl(Si03)2 and (Fe- Mg)Si(X$. It is essentially u mixture of the cum- 
mmgtomte molecule with one corresponding to the jadeite xnolecul' 



ANHYDROUS METASILICATES 391 

among the pyroxenes An analysis of a specimen of katofonte (com- 
pare p 387) from the samdmite bombs in the lava at Sao Miguel, Azores, 
is quoted in line I for comparison with the two glaucophane analyses in 
lines II and III 



Si0 2 AbOs FeaOa FcO MgO CaO Na 2 K 2 Total 

I- 45 S3 4 10 9 35 2 3 72 2 46 4 89 6 07 88 99 96 

IL 56 65 12 31 3 01 4 58 12 29 2 20 7 93 i 05 100 02 

III. 56 71 15 14 9 ?8 4 3 1 4 33 4 80 4 83 25 100 15 

I Kalofonlc, Sao Miguel, A/,orcb Also 2 96 per (cut TiOa 
II Glaucophane, lie dc Groi\ 
III Glaucoplunc, Shikoku, Japan. 

Glaucophane is rarely found in ciystals with end faces Even when 
these exist they are lough and yield poor measurements 

The mineral occurs in columnar crystals, in needles and in foliated 
or granular aggregates in rocks Their prismatic planes are oo p 66 (100), 
oo P ob (oio) and oo P(iio) P(7n) and oP(ooi) are the only termina- 
tions that have been identified The cleavage angle is about 55 20'. 

Glaucophane is blue or bluish black, translucent and strongly pleo- 
chroic in yellowish, violet and blue tints. Its streak is grayish blue, 
its fracture uneven, its hardness about 6 and its density 3 Its refractive 
indices for yellow light arc a= i 6212, j8 1.6381, 7= 1.6300 

Before the blowpipe the mineral turns brown and then mdU to an 
olive-green glass It is difficultly attacked by acids. 

Glaucophane is distinguished from the other amphiboloids by its 
color, and from other blue silicates by its crystallization, hardness and 
manner of occurrence, 

It is usually unaltered but it has been described m one instance as 
being partially changed to chlorite 

Synihews It has not been produced artificially. 

Occurrence The mineral is found only in metamorphosed limestones, 
in mica schists and in the garnet rock known as eclogite. It is charac- 
teristically a metamorphic mineral 

Localities.' Glaucophane occurs m long crystals in various schists in 
Syra, Cyclades, Greece; in hornblende schists in the He de Groix, Brit- 
tany, France, in a glaucophane schist on the Island of Shikoku, Japan, 
and abundantly in various schists m the Coast Ranges of California, 



392 DESCRIPTIVE MINERALOGY 

Arfvedsonite, Riebeckite and Crocidohte 

These amphiboles are comparatively rare They occiu principally 
in coarse-grained alkalme igneous rocks, usually as prismatic grams 
without terminations, embedded in the lock mass Arfvcclsomtc, how- 
ever, m some cases, occuis in groups of crystals on some of which tei- 
minations can be identified 

Riebeckite, NaFe(S Oa)2, has a composition veiy near that of acmite, 
and crocidohte contains, in addition, the molecule FcSiOa Ai fvodsomte 
is much more complex than either of these and has no equivalent among 
the pyroxenes Analyses of typical specimens of the two minerals aie 
quoted below In line IV is an analysis of crocidohte 



Si0 2 A1 2 3 


Fe 2 3 


FeO MgO 


CaO 


kjO 


NaoO 


IIoO 


Total 


I 


47 08 


i 44 


i 70 


35 


65 




2 32 


2 88 


7 14 


2 08 


100 29 


II 


49 6 S 


i 34 


17 66 


*9 


55 




3 16 




7 61 


i 6 7 


100 64 


III 


50 01 




28 30 


9 


37 


34 


i 32 


72 


8 70 




90 98 


IV 


S 1 3 




17 88 


21 


19 


09 






6 41 


3 c >4 


100 24 



I Black arfvedsonitc, Kangcrdluarsuk, Greenland 

II Riebeckite from granite, Qumcy, Mdbs 

III Riebeckite from Socotra, Indian Ocean 

IV Bark blue radial aggregates of crocidohte, Cumberland, R. I 

Arfvedsonite is usually in long prisms flattened parallel to 
oo P So (oio), but otherwise very much like hornblende. It m block or 
dark green and translucent, and has a dark bluish gi ay st rcaL It s hard- 
ness is 6 and density 3 4-3 5 rt 1S strongly plcochroic Thin splinters 
parallel to oopSb (oio), are olive giccn and those paialM to oo I>6b 
are deep greenish blue Its refractive indices for yellow light are: 

05=1687, 0=1707, 7=i7S 

Before the blowpipe the mineral fuses easily to <i black magnetic 
globule and colors the flame yellow It is not acted upon by acids. 

Riebeckite is found only in embedded prisms, showing no termina- 
tions It is black, vitreous and very plcochroic m gieen and dark blue 
tints Its density is about 3 3, and its hardness 5.5-6. Its reft active 
index for yellow light is about i 687. Before the blowpipe it fuses easily, 
imparting an intense yellow color to the flame. 

Crocidohte is an asbestus-hke, lavender-blue or dark green nebeckitc, 
that contains a larger amount of iron, due to the presence of the mole- 
cule FeSiOa It occurs also in earthy masses. Itb st reak is lavender-blue 
or leek-green and its hardness is 4 In all cases it appears to be a 
secondary mineral, The green fibrous variety ib known as " catVeye." 



ANHYDROUS METASILICATES 393 

Both nebeckite and: rfvedsomte weather to aggregates of iron oxides, 
quartz and carbonates The decomposed, brown crocidolite is the well- 
known ornamental stone " tiger's-eye " 

Occurrence and Localities Arfvedsonite is found principally in 
igneous rocks rich in soda, especially the coarse, nephelme syenites of 
Greenland, Kola, Russia, and m the augite syenites of Norway. It 
occurs also in the nephelme syenites of Dungannon township, Ontario, 
and of the Trans-Pecos district, Texas 

Riebeckite is also formed m acid locks nch in soda, such as certain 
giamtes, syenites, etc It is found on the Island of Socotia in the Indian 
Ocean, in fine-gramecl granitic locks at Ailsa Crag, Scotland, m Corsica 
and a few other places The crocidolite variety occurs in a clay slate 
on the banks of the Orange River in South Africa, at various pomts in 
the Vosges, Salzbuig, Tyrol and Andalusia, in Europe, in Templeton, 
Ontano, in veins at Beacon Pole Hill, near Cumberland, R I , m gran- 
ites at Quincy and Cape Anne, Mass , near St Peter's Dome, El Paso 
Co , Colorado, and as fibers in rocks at various other points m the United 
States, 

TR1CUN1C AMPHIBOLE 

The only known tnclmic amphibole is the comparatively rare aenig- 
matite, an alkali amphibole with a complicated composition that may 
be represented by the formula Na4Feq(Al-Fe) 2 (Si Ti) 12 O3s The 
mineial occurs m very complex crystals, with noAiTo=66, in 
alkdlinc rocks at Naujakasik, Greenland, m the Fourch Mts , Ark ; 
and at several other places 

It is black, or brownish black, and translucent or transparent and 
has a reddish brown streak It is, moreover, strongly pleochroic m 
brownish black and reddish blown tints It is brittle, has a hardness 
of a little more than 5 and a density of 3 7-3 8 Before the blowpipe it 
fuses to a brownish black glass It is partly decomposed by acids It 
is distinguished from other dork hornblendes by the cleavage angle 
of 66. 

BASIC METASILICATES 
Kyamte ((A10) 2 SiO 3 ) 

Kyanite, cyamte, or disthene, is a fairly common product of meta- 
moiphisni in certain schists The name kyamte suggests the sky blue 
color noticed in many specimens The name disthene refers to the 
great difference in hardness exhibited m different directions. 

The mineral is regarded as a basic metasihcate of the theoretical 



394 



DESCRIPTIVE MINERALOGY 



composition 8102=3702, ^203 = 6298 (compare pages 319, 320). 
Nearly all specimens contain a little FeaOs but otherwise they cor- 
respond very closely to the calculated composition indicated by the 
above formula A light blue specimen from North Thompson River, 
B C , upon analyses, gave 

Fe 2 3 CaO MgO Total 



Si0 2 
36 29 



A1 2 3 
62 25 



55 



i 06 



100 51 



7=io S 44l' 




' c _^ 




. 


J . 




' a 





FIG 210 -Kyamte Crys- 
tal with oo PQO, ioo (0), 

oo POO, oio (ft), oP, 
ooi (c), co'P, 1 10 (Jf) f 

oo P', no (m) and 

00 P'2, 210 (I)' 



Kyamte crystallizes m the tnchmc system (luclinic piruicoiddl 
class), with an axial ratio 8991 i 709* = 9 Si', 0= 101 2' and 
Very few crystals are well developed Their habit is 
columnar or tabular with oo P 66 (ioo) predomi- 
nating More frequently the mineral occurs 
in long, flat, isolated blades, or in diveigmg 
flat plates (Fig 210) Some crystals are 
very complex. Usually, however, only the 
forms oo Poo (ioo), ooPoo(oio), ooP'(no), 
oo'P2(2io)j oo'P(iTo) and oP(oor) arc pres- 
ent Twinning is common according to several 
laws, most of which, however, yield twins in 
which the basal planes (oP) of the twinned in- 
dividuals are parallel The most frequent 
twins have oo P 65 (ioo) as the twinning plane 
Other twinning planes are perpendicular to the axis c, or to the 
axis b The basal plane oP(ooi) also serves as the twinning plane 
m some cases Twinning is often repeated, producing lamellae crossing 
columnar crystals approximately parallel to the basal plane, and giving 
rise to a definite parting in this direction 

The cleavage of kyamte is very perfect parallel to oop65(ioo) 
and less perfect parallel to co P 06 (oio) It frequently possesses also a 
parting parallel to oP(ooi), as already stated The luster on cleavage 
faces is pearly Otherwise it is glassy. The mineral is often hght blue 
in color, less frequently it is colorless or white, yellow, green, brown or 
gray It is translucent or transparent and the darker blue varieties are 
pleochroic m dark and light blue tints. Its hardness varies greatly 
on different faces and in different directions on the same face. On the 
macropmacoid a it is about 5 parallel to the vertical edges, and 7 in the 
direction at right angles to this The specific gravity of the mineral is 
about 36, and its refractive indices for yellow light are; a 2=1.71 71, 
l8=;i 7222,7=1.7290. 

Before the blowpipe kyanite whitens, but otherwise it reacts like 



ANHYDROUS METASILICATES 



395 



sillimamte It is insoluble m acids It is distinguished from the few 
other minerals that it resembles by the great differences in hardness on 
its cleavage surfaces At a high temperature (about 1350) it appar- 
ently changes to silhmanite 

Kyanite weathers to muscovite, talc (p 401) and pyrophylhte 
(p 406), and is itself an alteration product of andalusite and corundum 

Synthesis It is not known that the mineral has been produced in the 
laboratory 

Occurrence and Origin Kyanite occurs as large plates and small 




FTO 2TT Bladcrl Kyanito Crystals in a IV! u m cons Quart/, &< hist from PM/O Forno, 
hwiUcrlaml (About natural st/e ) 

crystals in micaceous and othei schists (Fig 211), and as an important 
constituent of some quarUites At Horrsjoborg, m Wermland, Sweden, 
it forms a distinct layer of schist several meters thick In a few places 
it is found m zones of contact metamorphism, but it is more frequently 
the result of dynamic metamorphism (cf p. 26). 

Locates Crystals have been found at Gremcr in the Tyrol, at 
Mte Campione in Switzerland, and at Graves Mt m Lincoln Co , Ga 
The mineral also occurs in fine plates at Chesterfield, Mass , at Litch- 
field, Conn,; at Bakersvillc, N. C, and on North Thompson River, 
B C , Canada 

Uses Transparent kyanite is sometimes used as a gem. 



396 



DESCRIPTIVE MINERALOGY 



Calamine ((ZnOH) 2 SiO 3 ) 

Calamme, or hemimorplute, is an important ore of zinc It is one of 
the few silicates used as a source of metals While theoretically a 
pure zinc compound it usually contains a little FcjO? and ficquently 
small quantities of PbO In some cases it contains also a little carbon- 
ate A number of formulas have been suggested foi it, of which the 
one given above is the simplest According to several piommcnl mmei- 
alogists, howevei, the formula ZnaSiO4 HaO is prof ci able 

Si0 2 FeoOj ZnO HjO Total 

Theoretical 25 01 67 49 7 50 100 oo 

WytheCo, Va 23 95 6 7 8S 8 H 99 9<> 

Fnedensville, Pa 24 32 2 12 65 05 7 89 99 38 

The mineral occurs in brilliant crystals that are orthoihomlnc and 
distinctly heniimorphic (rhombic pyramidal class), with an axial uitio 

of 7834 i .4778 The crystals 
are usua lly tabular parallel to 
<*>P&(oio) Many ate highly 
modified but some are fairly sim- 
ple, with oo P(i 10) , oo P 66 (TOO) 
and 3? 05(301) m the pris- 
matic zone, 3Po6 (031), Poo (101), 
Poo (on) and oP(oot) at the ana- 
logue pole and ^P2(i2j) at the 
antilogue pole (Fig 212) The angle 
no A no 76 c/ Tunis are fanly 
common, with oP(ooi) the twinning 
plane Often many crystals sue 
grouped in sheaf-like, lilmms 01 
warty aggiegates and in crusts The mineral is also granular and 
compact Its cleavage is perfect parallel to oo p(i 10) 

Calamme is glassy, transparent or translucent, and when pure is 
colorless or white Usually, however, it is gray, yellow, brown, greenish 
or bluish Its streak is white, its hardness 4-4 5 and its density 3.2 3 5 
It is brittle Its fracture is uneven The mineral is strongly pyroelec trie 
with the end of the crystals terminated by dome faces the analogue pole. 
In contact twins both ends are analogues. The mineral becomes phos- 
phorescent upon rubbing, and is fiuoiescent m ultra violet light. Its 
refractive indices for yellow light are ot- 1 6136, 0= r 6170, 7=1 6360. 
Before the blowpipe calamme is almost infusible, but on charcoal 
it swells, colors the flame greenish and fuses with difficulty on the edges* 




FIG 212 Calamme Crystals with oo P, 
no (m), oo P56, 100 (a), >po6, 
oio (6), 2P*2, 12! (i)), Poo , 101 (A), 
Poo, on (e), 3P3oi Wi 3P, 
031 (0 and oP, ooi (c) 



ANHYDROUS METASILICATES 397 

With soda it gives the zinc sublimate In the closed glass tube it de- 
crepitates and yields water and becomes cloudy Its powder dissolves 
in even weak acids with the production of gelatinous silica 

Calamme is distinguished from smithsomte by its reaction with acids 
and from other minerals by its crystallization and reaction for zinc It 
alters to willemite, smithsomte and quartz Calamme has not been 
produced artificially 

Occurrence It occurs principally in the upper or oxidized zones of 
veins of zinc ore and in layers above the zone of permanent ground water 
in certain zinc and lead-bearing limestones It is associated with lead 
ores and various zinc compound^ and it often pseudomorphs calcite, 
galena and pyromorphite 

Localities Calamme occurs in nearly all places where zinc and 
lead ores arc found It is abundant at Altenberg near Aachen in Rhen- 
ish Prussia, at Wiesloch, in Baden, near Tamowitz, in Silesia, at 
Rezbanya, Hungary, near Bleiberg., Cannthia, near Santander, Spain, 
in Cumberland, England, at Sterling Hill, N J , at Fnedensville, 
near South Bethlehem, Penn , at the Bertha Mine in Pulaski Co , and 
at the Austin Mine, in Wythe Co , Va , and in the zinc-producing areas 
in the Mississippi Valley 

Usett It is a common a-bbociate of other zinc ores and many lead 
ores and is mined with the former as a source of zinc. 

ACID METASILICATES 

SERPENTINE GROUP 

The serpentine group includes a large number of hydrous magnesium 
silicates that differ from one another mainly in the proportions of water 
present and m the ratio of silica to magnesia None of them yields 
crystals, though their crystallization is thought to be monoclmic All 
occur in dense fibrous or platy aggregates The most prominent mem- 
bers of the group are 



Serpentine BUMgaSigOo, or Si02 MgO 

H(MgOH),<(Si0 3 )2 =43 'So 4346 1304 

Meerschaum. . HUMgsSisO i o, or 

H 3 Mg(MgOH) (8103)3 =60 83 27 01 12 16 

Steatite . H2Mgij(SiOs)i "63 52 31 72 4 76 

All are soft and nearly infusible, and all are of considerable economic 
importance. 



398 DESCRIPTIVE MINERALOGY 

Serpentine (H 4 Mg 3 Si2O 9 ) 

The substance known as serpentine may be two different minerals, 
one orthorhombic and the other monochmc They, however, cannot 
be distinguished, except by microscopic study Serpentine occurs in 
structureless, fibrous, foliated and schistose masses of a white, gray, 
brown or green color It is translucent and has a dull, slightly glistening 
or fatty luster, and a white streak The variety known as " noble ser- 
pentine" is nearly transparent and has a clear gieemsh or yellowish 
white, yellowish green, apple-green or dark green color The mineral, 
when pure, has a hardness of 3, but it frequently seems harder because 
there are often mixed with it tiny remnants of the much harder minerals 
from which it was derived The specific gravity of pure serpentine is 
2 5-2 6 Its refractive indices vary widely /3= i 502-1 570 

Serpentine fuses on thin edges when heated in the blowpipe flame 
It yields water in the closed tube When heated to about 1400 it crys- 
tallizes as olivme It is decomposed by hydrochloric and sulphuric 
acids with the separation of gelatinous silica, which, m fibrous* varieties, 
retains the shapes of the fibers. It is also soluble in dilute carbonic acid 
Its powder reacts alkaline 

Chrysolite is a silky, nearly transparent fibrous variety occurring in 
veins It is apparently orthorhombic. 

Antigonte is a form occurring m laminated masses or in microscopic 
scales, that are possibly monochmc 

Baltwnonte and ficrolite are coarse, green, fibrous varieties 

Analyses of a pure green serpentine, and a typical chrysotde, both 
from Montville, N J , are quoted below 

Si0 2 A1 2 3 Fc 2 3 FeO MgO CaO H 2 O Total 

I 42 05 30 .10 42 57 05 14 66 99 73 

II 42 42 63 62 . 41 01 15 64 100.55 

I Green serpentine, Montville, N J 
II Chrysotile, Montville, N J Also 33 NiO. 

Massive varieties are distinguished from tak by their solubility in 
acids and by differences m hardness, and chrysotile is distinguished from 
ampkibok asbestus by the presence in it of water, 

Synthesis. Serpentine has been made by the action of a solution of 
Na2SiOs upon magnesite for 10 days at 100. 

Occurrence The mineral is a common decomposition product of 
several other magnesium silicates, more particularly olivine, pyroxene 



ANHYDROUS METASILICATES 399 

and chondrodite Many igneous rocks rich in these minerals are com- 
pletely changed to serpentine, especially around their peripheries, and 
some metamorphosed limestones are also partially or completely ser- 
pentimzed It is probably a secondary mineral in all cases 

Localities Serpentine occurs in large quantity at Webster, N C , 
Montville, N J , Easton, Penn , at the Tilly Foster Iron Mine, 
Brewster, N. Y , at Thetford and Black Lake in the Eastern Townships 
of Quebec, and at many other places m North America, It is also known 
fiom many places in Europe 

Uses Serpentine when massive is used as a building stone The 
finer varieties are sawed into thin slabs and used for ornamental purposes 
Marble with streaks and spots of serpentine is known as ophicdcite and 
under the name "verd-antique " is employed as an ornamental stone. 
Mixtures of serpentine with other soft minerals are ground for a paper 
pulp The fibrous variety chrysotile is mined and sold under the 
name of asbestos, which, because of its fibrous structure, its flexibility, 
its incombustibility, and because it is a nonconductor of heat and 
electricity is becoming an exceedingly important economic product. It 
is woven into paper and boards that rrc used to cover steam pipes, and 
to increase electric insulations, and is manufactured into shingles It 
is used also in fireproofing, m the manufacture of automobile tires, 
in making paints, and as a substitute for rubber in packing steam 
pipes 

Preparation The chrysotile mined in Vermont comes from a mass 
of serpentine that its cut by many small veins of chrysotile The rock is 
crushed and the liber is separated by washing, or by some other mechan- 
ical method The pulp rock at Easton is a mass of serpentine, talc and 
a few other minerals It is ground and sixed for use in paper manu- 
facture 

Production Chrysotile is mined in Vermont and Wyoming. The 
production is rapidly increasing but the actual amount mined annually 
has not been disclosed. The total aggregate of chrysotile and amphibole 
asbestos (see p. 386), produced in the United States during 1912 was 
4403 tons, valued at $87,959 The imports of unmanufactured asbestos 
for the same year were valued at $1,456,012, of which $1,441,475 worth 
came from Canada. The total production of this country m the same 
year amounted to about $2,979,384, most of which came from the Thet- 
ford district in Quebec. This is about 80 per cent of the world's pro- 
duction. The value of the serpentine used as an ornamental and build- 
ing btonc is not known, 



MgO 


A1 2 Fc 2 3 


H 2 


Total 


2 47 


S 


is ss 


99 


10 66 


i 57 


IS 83 


99 75 


18 27 


.89 


15 40 


99 08 



400 DESCRIPTIVE MINERALOGY 



Garnierite 

Garmente may be regarded as a serpentine or talc in which a portion 
of the magnesium has been replaced by nickel, or possibly as a mixture 
of a colloidal magnesium silicate and a nickel compound Its impor- 
tance consists in the fact that it is the only commercial source of nickel 
aside from the pentlandite in the pyrrhotite of Sudbury, Canada. 
Three analyses of garmerite from New Caledonia follow. 

Si0 2 NiO 

35 45 4S IS 

37 78 33 9i 

42 61 21 91 

These show that as MgO diminishes, NiO increases. 

Garmerite is a dark green to pale green substance with many of the 
physical properties of serpentine Its luster is dull, or like that of var- 
nish It has a greasy feel, a hardness of 2-3 and a density of 2 3-2 8 
Its streak is light green to white When touched to the tongue it ad- 
heres like clay It is infusible when heated before the blowpipe, but 
decrepitates and becomes magnetic. It is partly soluble in HCl and 
HN0 3 

It is readily distinguished from malachite and chrywcolfa by its 
structure, its greasy feel and the absence of a good copper test. 

Occurrence and Localities The mineral occurs as earthy masses, as 
mamillary coatings and as impregnations and veins in serpentine. In 
all cases it appears to have resulted from the weathering of periclotite. 
The earthy masses are residual and the veins are deposits from down- 
ward percolating water that obtained nickel from the decomposing 
rock 

The principal occurrences of garnierite are New Caledonia, where it is 
mined as a source of nickel, and at Riddles, Douglas Co,, Oregon, A 
very closely allied species, genthite, occurs associated with chromitc in 
serpentine at Texas, Lancaster Co,, Perm., at Webster, N. C., at Malaga, 
in Spain, and at a few other places 

Production Garniente is mined from 40 mines on the plateau of 
Thio, New Caledonia, at the rate of about 130,000 tons annually of a 
6| per cent ore. In 1912 there were produced 72,315 tons of ore and 
5,097 tons of matte containing 2,263 tons * nickeL The aggregate 
value of ore and matte was about $1,140,000, 



ANHYDROUS METAHIIJCATES 401 

Meerschaum (H 4 Mg2Si 3 Oio) 

Meerschaum, or scpiohte, occurs as a massive, dense, earthy aggre 
gate of a white, yellowish or reddish color, and also as a finely fibrous, 
crystalline aggregate (parade piohte) It is opaque, has a conchoidal 
fracture and a shining white streak Its hardness is 2 and density 
about 2 Dry specimens will float on water, because they are not 
easily wet When touched to the tongue a clinging sensation is pro- 
duced Two varieties of the commercial material have been recognized 
Of these, one, a sepiohte, is HsM^SiaOi*) and the other j8 sepiolite, 
has the composition indicated above 

The analyses of white meerschaum irom Asia Minor and from Utah 
gave the following results 



Al 2 0j Fe 2 0j MgO H 2 O Total 

Asia Minor 52 4$ 80 23 25 23 50 100 oo 

Utah 52 97 86 70 22 50 18 70 * 99 74 

* Of this 8 80% was driven off at 100, Included also tire 3 14 Mn 2 0j and 87 CuO 

Before the blowpipe the mineral fuses on its edges to a white enamel 
Often, at first, it tuins brown 01 black and then, upon higher heating, 
it bleaches to white At low temperatine in the ebbed tube it yields 
a little hygiostopic water. At high temperature water is given off fieely 
The mineral dissolves m hydicx hlouc auci, with the production of gelat- 
inous silica m the case of theot variety 

Meerschaum resembles chalk and kaolin, from which it is easily dis- 
tinguished by treatment with hydrochloric acid. 

Occurrence and Localities The mineral is found as nodules in young 
sedimentary beds in Asia Minor, where it is associated with magnesite. 
Both minerals are believed to be alteration products of serpentine It 
occurs also with opal at Thebes, Greece. A iccl variety occurs in lime- 
stone at Qumcy, France, and a green and white variety forms a small 
vein m a silver ore in Utah In nil of its occurrences it seems to be 
secondary 

Cfre^ -Mecrathaum is used for carving into ornaments and pipes. 

Steatite (HaMgaCSiOaM 

Steatite, or talc, usually occurs in flaky, foliated and massive forms, 
and in plates that appear to be tabular crystals with hexagonal outlines, 
It also forms, with chlorite and a few other substances, the rock soap- 
stone. Although its crystallisation is unknown, because of the close 



402 DESCRIPTIVE MINERALOGY 

analogy between its physical properties and those of chlorite and the 
micas its symmetry is believed to be monoclmic 

The composition of pure white talc and ordinary soapstone are shown 
by the two analyses below 

White tile Soapstone 

Urserenthal, Switrerlanil W Gnqualand, Africa 

Si02 o 8 5 6 3 2 9 

A1 2 3 i 7i * 24 

Fe 2 3 

FeO 09 

MgO 32 08 

H 2 4 9S 

Total 99 68 100 90 




The composition corresponding to the formula HjMg^SiOa)! is- 
Si0 2 =63 5, MgO=3i 7 and H 3 0=4 8 

The cleavage of talc is well marked and on its cleavage surfaces its 
luster is pearly Its cleavage plates arc flexible The mineral is white, 
gray, greenish or bluish, and is transparent or ti anslucent The massive 
forms, known as soapstone, aie white, gicenish, yellowish, red or brown 
All varieties are soft the mineral being chosen to represent r m the 
scale of hardness and all have a soapy feeling The density of pure 
talc is 2 6-2 8 For yellow light, a i (530, #= i 589, 7*= i 1589. 

Before the blowpipe the mineral exfoliates, hardens and glows 
brightly, but it is nearly infusible (fusing temperature is about 15^0), 
melting only on the thinnest edges to a white enamel. It yields water in 
the closed tube only at a high temperatuie. It is unattacked by acids 
before and after heating Its powder reacts alkaline. 

It is distinguished from other white, soft minerals by its softness, its 
insolubility in acids and its infusibihty 

Occurrence The mineral is a common alteration product of other 
magnesium silicates, often pseudomorphing them. Thus, pseudo- 
morphs of the mineral after actmolite, Imnuite and siihlite are common 
Pseudomorphs after pectolite, dolomite and quarto are also known. In. 
these forms it is secondary. 

It occurs also m marbles and other crystalline rocks, where it was 
produced by regional metamorphism, It is found, further, as small veins 
cutting serpentine and metamorphosed limestones, as layers under the 
name of talc schists, associated with other schistose rocks and as massive 
aggregates of finely matted fibers, probably resulting from the alteration 
of basic igneous rocks The last described variety is the rock soapstone. 



ANHYDROUS METASILICATES 403 

The vein material is usually white, fibrous and pure It is gi< und and 
placed on the market as talc The impure \ ai icty (soapstone) is sawn 
into blocks and boards 

Localities Talc and soapstone occur at many places Good white 
platy talc occurs at Lampersdorf, in Silesia, near Piessnit?, m Bohemia, 
near Mautern, m Steiermark, at Andermatt, in Switzeiland, at Russell, 
Gouverneur and other points m New York, at Webster, N C , and at 
Easton, Penn 

U$e\ Ground talc is extensively used as a lubricator, m the manu- 
facture of papci, as a fillci m curtains, cloth, etc , as a foundry facing, in 
the manufacture of molded rubber goods, ub a toilet powder, as a polish- 
ing material, as a pigment, in the manufacture of gas tips, pencils, cray- 
ons, etc Soapstone is sawn and used as linings of acid vats and laundry 
tubs, and in the manufacture of table tops, sinks, etc , in chemical labora- 
tories Because of itb nonabsorbent qualities it is also being used 
largely in electric switchboards. Its various uses are due to its softness, 
mfusibility, and its power of resistance to the attacks of acids 

Production. The principal sources of talc and soapstone m the 
United States are m a belt on the east side of the Appalachians ex- 
tending from Vermont to Georgia Largest producers m 1912 were: 

Virginia, wilh a production of 25,313 tons, valued at $576,473, 
New York, with a production of 66,867 tons, valued at $656,270, 
Vermont, with a pioduclion of 42,413 tons, valued at $275,679 

Of the aggregate of 159,270 tons, valued at $1,706,963 produced m 1912, 
15,510 tont. were sold in the rough for $66,798, 2,642 tons, sawed into 
slabs, were sold for $50,334, 21,557 tons were manufactured and sold for 
$600,105, and 119,561 tons were sold ground for $989,726. Of this 
aggregate 133,289 tons, valued at $1,097,483 were talc and 25,981 tons, 
valued ai. $609,480 were soapstone In addition to the home produc- 
tion, there were also consumed in the United States 10,989 tons of high- 
grade talc, valued at $122,956, which was imported, 

KAOLIN1TK GROUP 

The kuohnitc group of minerals comprises hydrous aluminium sili- 
cates corresponding to the magnesium silicates of the serpentine group 
The principal members of the group are* 

Kaohmte, HiAbSfeOo, or H 2 Al(Al(OH)3)a(Si0 3 )4 

=346,50 Si0 2 , 39 S 6 A kO> *3 94 H 2 
Pyrophyllite, HzA,h(SiQz)4 66,65 SiOa, 28 35 AlsOs, 5 oo H 2 



404 DESCRIPTIVE MINERALOGY 

Kaolmite corresponds to serpentine in which all the Mg has been re- 
placed by Al and pyrophyllite to steatite In addition to these, there 
are other closely related compounds which may be intei mediate in com- 
position between these two Among them the most common arc allo- 
phbne, montmonllonite and hallo vwtc 

Both minerals are of economic importance Kaohmte is the base 
of all clay products like pottery, tile, bnckb, etc 



Kaolinite 

The crystallization of kaohnile is piobably jnonoc hnu The ciystals, 
which are rare, are thin plates with an hexagonal habit, bounded by the 
planes oP(ooi), ooP(no) and ooP> (oio) and +P(7ii). Thou axial 
ratio is 5748 ' i : i 5997 with =83 n'. Their cleavage is peifect 
parallel to the base 

Distinct crystals have been found only on the Island of Anglesey, 
Wales, and at the National Belle Mine, at Silveiton, Colo , wheie they 
comprise a white powder eveiy grain of which is a ciystal 

The mineral, when pure, is white or colorless and transparent. It 
has a hardness of i and a specific gravity of 2 45 It is infusible before 
the blowpipe and is only slightly attacked by HC1 It is decomposed 
by alkalies and alkaline carbonates with the production of hydratcd 
silicates Its index of refi action is about i 56. 

The greater part of the kaolmite known is not in nystuls ft usually 
occurs in foliated or dense earthy masses to which various names have 
been assigned 

Naknte is a white crystalline mass of kaolmite made up of tiny 
flakes often arranged in fan-like or divergent groups. The individual 
flakes have a pearly lustei It occurs as vein lillmgs in certain ore- 
bodies 

St&nmarkite is a dense mass of microscopic grains often forming 
nodular masses and occurring as veins ancl nests in rocks. It is harrier 
than pure kaolin (H 2-3), and is often yellowish, gray or reel in color 

Kaohn is an earthy, friable mass of flaky kaolmite which when moist 
becomes plastic, and, therefore, of great value in the manufacture of 
pottery It is more soluble in acids than the crystallised variety. It 
fuses at about 1780 

Kaolin is distinguished from chalk by its reaction toward HC1, from 
meerschaum and talc by the reaction for Al with Co (NO;*) a, and front 
mfusional earth by the fact that its powder will not scratch glass, 

Clay is a mixture of kaolinite, quartz, fragments of other mineral 



ANHYDEOUS METASILICATES 405 

particles and various decomposition products of kaohmte and other 
silicates, among the most important being various colloidal, hydrous, 
aluminous silicates and magnesium and calcium carbonates The 
gieater the proportion of colloidal material in the clay the more plastic 
it is and the more valuable lor manufacturing purposes Different clays 
have received diffei ent names which indicate in a way their uses Among 
the most impoitant of these arc 

China day, a very puie, white kaolin, 
Ball day, a white, very plastic clay, 
Fje day, a fanly pure clay capable of resisting great heat, 
Flint day, a hard clay which is not plastic even after grinding, 
Brick day, an impure clay suitable foi making brick, 
Pottety day, stoneware clay, terracotta day, etc , are jU impure clays 
that are adapted to the uses suggested by their names 

Sample analyses of kaohmte and of some of the purer clays follow 

F Total 
IS ioo n 
100 oo 

100 00 

99 97 



Si02 AbOa FcsOj CaO Nd20 


HjO 


I 46 35 39 59 ii IS 


13 93 


II 46 86 39 24 


13 90 


III 43 46 41 48 i 20 37 


13 49 


IV 59 92 27 56 i 03 tr. ,64 * 


10 82 


F Crystals Fiom National IH!e Mine, Colo 




II Kaolin, SuliU, near Meissen, Saxony 




Til Slemmfiikile, S< hlaKgcnwalil, Hohc-muu 




IV Flint lire i lay, Salmeville, Ohio. 




* NujO+KjQ 





Occurrence Kaohmte occurs in feldspathic rocks near ore veins, 
Here it was foimccl partly by ascending magmalic solutions and partly 
by descending IIgS04, produced by the oxidation of the sulphides In 
the uppci poi lions of the veins Most kaolin, however, is a weathering 
product of feldspar (see p. 408), and of feldspathic rocks. When 
acted upon by water, and more particularly by water containing dis- 
solved CDs, the feldspars lose alkalies, calcium and some silica, leaving 
an aluminium silicate behind. Thus, for the potash feldspar orthoclase. 



AlaO,* 6SiOi( KAlBLAt) - K a O * 48102 Al20;j sSiOu, which with 
(kaolimte). 



Other silicates also yield kaohmte on weathering in some cases 
completely changing so as to yield pseudoinorphs of kaolin. 

Very complete weathering of this kind takes place in bogs, and 



406 DESCRIPTIVE MINERALOGY 

some of the best known beds of kaolin arc believed to have been formed 
at the bottoms of peat bogs 

Locakhes Kaohnite in measurable crystals occurs only at the two 
localities that have already been mentioned The puic, white, dense 
kaolin is fairly widely spread Clay occuis almost um\ci sally The 
principal localities of kaolin in North America aie near Jacksonville, 
Ala , Mt Savage, Md , various points in Tennessee, Noith Carolina, 
Illinois, Missouri, New Jersey and Pennsylvania 

Production The total value of clay products manufacluiccl in the 
United States during 1912 was over $172,800,000, of which by far the 
largest part is represented by common brick, of which $51,706,000 worth 
were made Pottery followed with an output valued at $3 6 , 504,000 It 
is not possible to estimate the value of the clay represented in the man- 
ufactured product because in most cases the manufactui CM s mine their 
own clay and make no account of the raw material The quantity of 
clay mined m the United States and sold to manufacturer during 1012 
amounted to 2,530,000 tons, valued at $3,946,000, In 'addition, there 
were imported 334,655 tons of clay, valued at $1,952,000 

Pyrophyllite (H 2 Al 2 (SiO,j)4) 

Pyrophylhte nearly always occurs m groups of radiating 01 diveigmg 
fibers that are either orthorhombic or monochmc in crystallisation It 
may be isomorphous with steatite. The bundles of libers derive easily 
into flexible sheets that have a pearly luster on their cleavage faces 
When pure the mineral is light-colored m shades of yellow, gray 01 green 
It is transparent or translucent and has a greasy feel Dense, struc- 
tureless masses are known as agalmatohte. 

The mineral is very soft, about i Its density is 2.8 or 2,0 Before 
the blowpipe it melts on the edges to a white enamel and fibrous varieties 
exfoliate and swell Heated m the closed tube pyrophyllite assumes a 
silvery luster and gives off water. It is only partially soluble in IIC1, but 
is completely decomposed by Na2COs* 

It is best distinguished from ta'c by the reaction for aluminium, 

Synthesis Upon heating to 3oo-soo a mixture of SiOs>, AliAt and 
potassium silicate a mass is obtained which consists of aiulalusite, 
muscovite and pyrophyllite 

Occurrence and locator Pyrophyllite is found at a number of 
points m many different associations, where it is probably the result of 
weathering of other silicates Its principal localities in the United 
States are Graves Mt., Ga., Cotton Stone Mt., Deep River, Cur- 



ANHYDROUS METASILICATES 407 

bonton and Glenclon, N C , Chesterfield, S C , and Mahanoy City, 
Penn 

Uses The massive form of the mineral is used to some extent in 
making slate pencils, and for the other purpose for which talc is employed 
Agalmatohte is used by the Chinese as a medium from which they carve 
small images 



CHAPTER XVIII 

Tim SI LIC ATKS t ontmmd 

THE ANHYDROUS TRIMETASILICATES 

THE FELDSPARS 

THE feldspars are among the most impoitanl ol .ill mineials They 
are abundant as constituents of many igneous locks and in mixtures 
filling veins Their principal scientific impoitaiuo lies in the fact that 
they indicate by their composition the nature of the lock magmas from 
which they crystallize Consequently, in some systems of rock classi- 
fication the grouping of the rocks is based primarily upon the presence 
or absence of feldspar, and the naming of the fddsputhie rocks is in 
accordance with the nature of their most prominent feldspathic con- 
stituent Moreover, some of the feldspars aie of economic importance. 

Chemically, the feldspars may be regarded as isomorphous mixtures 
of the four compounds, KAlSuO^NaAlSiiOs, NajAlAlSioOs, CoAlAlSi a O 
and BaALAlSiaOs, each of which, except the third, has been found nearly 
pure in nature as orthoclase and murodme, barhimlt* and Mite, an- 
orthite and cdswn The third, Na2AlAlSioOs, has been mule m the 
laboratory, but it occurs in nature only in isomorphous mixtures with 
the anorthite and albite molecules The pure compound has been 
called carneg^e^te and its mixtures anemomitn The feldspars have 
also been regarded as salts of the acid HftAlSigOx in which the hy- 
drogen is replaced by various radicals, thus. (KSi)AlSijjOK, orthodase; 
(NaSi)AlSi 2 8 , albite, (CaAlJAlSiaOg, anorthite, and (BaAl)AlSijOs, 
celsian 

The potash molecule crystallines fiom magmas containing potas- 
sium, sodium and calcium, but it also frequently forms isomorphous 
mixtUres with the soda molecule and in some cases with the barium 
molecule Mixtures of the potash and calcium molecules are e\- 
tremely rare as minerals, but they have been formed experimentally 
in the laboratory The albite and the calcium molecules are usually 
intermixed Both are known in a nearly pure condition an minerals, 
but their mixtures are much more common Indeed they are BO common 
that they are separated from the other feldspars and formed into a clh- 

408 



ANHYDROUS TRIMETASILICATES 409 

tinct subgroup under the name of the plagwdaw group, with albite and 
anorthite as the two end members The plagioclases constitute the best 
known isomorphous series of compounds in the realm of mineralogy. 

The calculated compositions of pure orlhoclase (or microclme), 
albite, anorlhite and celsian with their specific gravities are 



K 2 Na 2 CaO BaO Sp Gr 

Orthoclasc 64 7 18 4 16 9 2 55 

Albite 68 7 TO 5 u 8 2 61 

Anorthite 43 2 36 7 20 i 2 76 

Celsian 32 o 27 2 41 8 3 34 

All the feldspars aic trichnic, but the pure potassium and sodium com- 
pounds, in addition to possessing distinct trichnic phases (micioclme and 
albite) occur also in crystals which, because of sub-microscopic twinning, 
(p 420) are apparently monochnic (oithoclase and barbiente) Usually 
the forms on orthoclasc arc designated by symbols that refer to the 
monoclmic a\es, but since the habits of all feldspars are the same they 
can be as readily understood when referred to the tnclimc axes The 
crystallographic constants for the members of the group that consist 
of unmixed molecules are 

7 Anglc(ooi)A(oio) 



*{ 



Celsian 


657 : 


i : 


554 


90 


S 





2' 


90 




Albite 


6335 - 


i * 


5577 


04 





3' 


116 





29' 


88 


9' 


Anorthite 


.6347 : 


i ' 


SSoi 


93 





1.3' 


115 





S3' 


9i 


12' 



90 

86 24' 
85 50' 

The simple ciystals of feldspar exhibit three habits, but on nearly all 
the same forms occur. These are oP(ooi), ooP 06(010), ooP'(no), 
oo'P(no), /P/ oo (101), 2/Py oo (201) and less commonly s/P' 00(021), 
2'Py & (QJ i), oo P/3(i3o), oo /P3(i3o), /P(I n), P/(i7i) and oo P 60 (100) 
In orthodase and the other apparently monochnic forms these symbols 
may be written oP, coPob, oo P, p*, 2Poo, 2P5b, oopj, P and 
oo poo (Figs. 213 and 214). There have, moreover, been reported on 
orthoclasc about oo other planes and on the plagioclases about 45;. Of 
these, however, a number are probably vicinal, as they have extremely 
large indices, 

The principal habits are the equidimensional, the columnar (Fig. 
213), and the tabular (Fig. 214) The tabular crystals are usually 
flattened parallel to oio The columnar forms are elongated parallel 
to the c or the a axes 



410 



DESCRIPTIVE MINERALOGY 



Twinning is common, according to five laws, and much less common 
according to several others Of the five common laws three apply to all 
the feldspars, and the remaining two to the tnclimc types alone The 
first three are the Carlsbad, the Manebach and the Baveno The other 
two are the albite and the penclme 

In Carlsbad twins, 100 is the twinning plane and usually oio is the 



/77\ 



% 

LLV 





FIG 213 FIG 214 

FIG 213 Orthoclase Crystals with oo P, no (m), w P w , oio (ft), oP, OOT (c) and 

aP 55 , 201 (y) 

FIG 214 Orthoclase Crystals with m, b, c and y as m Fig 213 Albo P oo , loi (c), 
P, in (0), oo P3 , 130 (a) and 2P 2b , 021 () 






^ 
\zw 




FIG 216 



FIG 215 

FIG 215 Carlsbad Interpenctration Twins of Orthoclase Twinning plane ia 00 P 5 

(100), composition face ooPw (oio) 
FIG 216 Contact Twin of Orthoclase According to the Carlsbad Law. 

composition face. The twinned parts may interpenetrate, as is usually 
the case (Fig 215), or they may he side by side forming a contact twin 
(Fig 216) If m the contact twins the planes Tot and ooi are equally 
prominent, since they are nearly equally inclined to the c axis the twin 
may be mistaken for a simple crystal (Fig. 216), In rare cases the 
composition face is 100 and the twinned parts are in contact, 



ANHYDROUS TBIMETAHILICATES 



411 



The Baveno twins are contact twins, with 021 the twinning and com- 
position planes (Fig 217) As the individuals are elongated parallel to 
the a axis the result of the twinning is a square prism with its ends 
crossed by a diagonal that separates the same forms on the two twinned 
individuals In some cases the twinning is repeated and a fourlmg 
results 

In Manebach twins, the twinning and composition plane is ooi 
These usually occur m columnar crystals elongated parallel to 0, or in 
tabular crystals flattened parallel to ooi or oio (Fig 218) 

Ccirlsbad, Baveno and Manebach twins, as has been stated, are com- 
mon to feldspars of both the monochmc and tnclmic phases, but the 
penclme and albite laws are found only in the tnclmic types The 





FIG 217 



FIG 218 



FK, 217 -lUveno Twin of Orthoclasc Twinning and composition plane, aP ob (021) 
Fid 218- M iintbiu h Twin of Orlhoi Use Twinning and composition plane, oP(ooi) 



description of these is, therefore, deferred until the plagioclases are 

CUSSed. 

Besides occurring in crystals, nearly all the feldspars are known also 
m gianular and platy masses 

The pure feldspars are coloileas and transparent or translucent, and 
all have a glassy luster which, on cleavage faces sometimes approaches 
pearly As usually found, the feldspars are white, pink, reddish, yellow- 
ish, gray, bluish or green Some specimens show a bluish white shimmer 
or opalescence (moonstone), and others a reddish spaikle (sunstonc), 
due to enclosures of other minerals or of lamellae of a different refractive 
index from that of the mam portion of the mass All have u white 
streak All possess a very perfect cleavage parallel to the base (ooi) 
and a scarcely less perfect one parallel to oio Their fracture is uneven 
to conchoitlal, and hardness 6 

Befoie the blowpipe fragmentb of the potash, barium, and calcium 



412 DESCRIPTIVE MINERALOGY 

feldspars are very difficultly fusible on their edges to a porous glass 
The soda feldspars are a little more easily fusible The fusing tempera- 
ture of albite is between 1200 and 1250, that of orthoclase approxi- 
mately 1300, and that of anorthite 1532 Anorthite is soluble in 
hydrochloric acid with the production of gelatinous silica. The other 
three feldspars are insoluble 

The feldspars are distinguished from othei minerals by their crys- 
tallization, their two nearly perfect cleavages approximately perpen- 
dicular to one another, and their hardness They are distinguished 
from one another by characters that will be indicated in the descriptions 
of the several varieties 

Feldspars rich in orthoclase and soda weathei fanly leadily to mus- 
covite, or kaolin and quartz The soda feldspars in some cases change 
to zeolites (p 445). With the addition of the calcium molecule calcite 
is often found in the weathering products. Under certain conditions, 
especially when in rocks containing magnesium and iion rmncuils, the 
calcium feldspars often change to a mixture of zoisite and albite, 01 a 
mixture of these with garnet, chlorite (p 428), epidote and otlici com- 
pounds This mixture is often designated by the name &an\wntr 

Syntheses All crystals of the feldspars, except those of pure albite 
and pure orthoclase (including microchnc), have been made by slowly 
cooling a dry fusion of their components m open cuinbles Albitc and 
orthoclase have been produced from similar fusions to \\hi<h tungstic 
acid, alkah-tungstates or phosphates, or alkali-fluoride ha\r been a dried 
They have also been produced with quart/ by fusion m the presence 
of moisture in closed tubes 

Occurrence and origm All except the barium feldspars occur as 
important constituents of most igneous and of many metamorphic 
rocks. They occur also abundantly in a few sandstones (sirkoses) and 
m a few water-deposited veins, and are found mound a few volcnnic 
craters as products of gaseous exhalations The barium feldspars are 
rare They have been seen only in dolomite associated with Imnte and 
tourmaline, in manganese ores and manganese epidote, and intergrown 
with albite in a pegmatite at Blue Hill, Delaware Co , Pa 

Witih. respect to origin feldspars may be primary separations from a 
magma, primary deposits from solutions, pneumatotytie deposits, or 
they may be the result of metasomatic process. They are common 
products of contact and regional metamorphism 

Uses The feldspars, though extremely abundant, have compara- 
tively few uses In the future the potash varieties may become a 
source of the potash salts used in the manufacture of fertilizers. At 



ANHYDROUS TRIMETASILICATES 413 

present the principal use of the feldspars is in the manufacture of por- 
celain and other white pottery products and enamel ware They are 
used as fluxes to bind together the grains of emery and carborundum 
in the making of grinding and cutting wheels, and are employed also in 
the manufacture of opalescent glass, artificial teeth, scouring soaps and 
" ready roofing " 

Production All the feldspar used in commerce comes from pegma- 
tites The total quantity produced for all purposes in the United States 
during 1912 amounted to 86,572 tons, valued at $520,562. Of this, 
26,462 tons were sold crude at a value of $89,001 and the balance 
ground The principal varieties mined are orthoclase, microchne and 
albite, though ohgoclase (a plagioclase rich m soda) is mined in small 
quantity. 

ALKALI FELDSPARS 

Orthockse and Microcline (KAlSbO?) 
Barbierite and Albite 



Orthoclase and microchne have the same chemical composition 
Both are potash feldspars, but both may contain sodium On the 
other hand barbiente and albite are both essentially soda feldspars but 
both usually contain some potassium In orthoclase the sodium is 
due to the admixture of the barbiente molecule, and m microchne to 
the presence of the albite molecule The soda-rich microchne is gen- 
erally known as anorthodase. The pure barbiente is not known to 
exibt as a mineral Analyses of these four varieties follow 



SiO 2 AlaO,i CnO K20 Na 2 HjjO Total 

I 63 80 21 00 13 80 I 40 IOO 00 

II 65 23 19 315 76 o 31 4 152 27 loo 00 

TIT 67 oo 10 12 78 i 15 ii 74 . QQ 70 

IV 66 18 IQ 52 36 13 03 01 ioo oo 

V 67 99 19 27 7<5 3 o5 6 23 oo 09 03 

VI. 68 ?8 10 62 31 39 10 81 09 99,82 

T OrthocUsc, Aclularia, Elba 

II Soda-orlhoclase, JDrachenfels, Prussia, Also ,56 BaO. 
lit. Burbiente, KrajjjcrtS, Norway 
IV. Microclmc, Ersby, Pargas, Finland. 

V Anorthoclase, from granite, Kekequabic Lake, Mmn Also 82 FcjOj and 

trace of MgO 
VI, Albite, from htchfieldile, Likhfiold, Maine. Also .23 FO and .09 MgO, 

Albite is described among the plagioclascs (p, 418), 



414 



DESCRIPTIVE MINERALOGY 



The most noticeable difference between orthoclase and miciocline 
is that the latter shows clearly its tnchnic symmetry by its twinning, 




FIG 219 Section of Microclme Viewed between Crossed Nicols The grating 
structure indicates twinning ( ifltv Rownbmck ) 

and its optical properties, while in orthoclisc the twinning is so 
minute as to be unobservable and the op1 ical properties arc similar to 
those of monochmc crystals This difference is best exhibited in thin 
sections when viewed m polaroed light under the 
microscope Under these conditions certain sec- 
tions of microclme exhibit series of light and dark 
bars crossing one another perpendicularly (Fig, 
219), while sections of orthoclase do not. The 
grating structure is due to repeated twinning 
according to the albite and pericline laws at the 
same time (p 419). If this method of twinning 
is present in orthoclase the lamellae are so 
minute that they cannot be seen even under 
high powers of the microscope 

Several names that refer to more or less dis- 
tinct varieties of the potash feldspars are in com- 
mon use The most important are* 



FIG 220 Adulana 
Crystal with m, b, 
c, s and x as m 
Figs 2x3 and 214 
Also fP 55, 203 fo) 



Adularia, a nearly pure orthoclase, that is nearly transparent, occur- 
ring in veins Its crystals have the characteristic habit illustrated in 

Fig 220 



ANHYDROUS TRIMETASILICATES 415 

Samdtne, a glassy soda orthoclase, occurring as large crystals often 
flattened parallel to oio, embedded in lavas 

Moonstone, a translucent adulana, exhibiting a pearly luster, with 
a very slight play of colors 

Sunstone, a translucent variety exhibiting reddish flashes from 
inclusions of mica, or other platy minerals 

Perthtte, parallel mtergrowths of thin lamellae of orthoclase and 
albite 

Microchne-perthite* parallel mtergrowths of lamellae of microclme 
and albite 

Oithoclase and the other pseudomonoclmic feldspars may be dis- 
tinguished from the distinctly tnclmic forms by the value of the cleavage 
angle which in orthoclase is 90, and in the tnclmic forms about 86, 
except in microclme (See p 409 ) The value of the angle noAi^o 
= 61 13' in orthoclase Its refractive indices for yellow light are. 
oj=i 519, #=i 524, 7=1 526 With the admixture of the albite mole- 
cule these values increase The sp gr of pure orthoclase is 2 55 and 
its fusing point a little higher than that of albite (see p. 412) 

Oithoclase may be distinguished from the other pseudomonoclimc 
feldspars by its specific gravity and the flame reaction 

Syntheses Crystals of orthoclase have been made by fusing 
SiOa and AkO* with potassium wolframate, vanadale or phosphate 
Also by heating aluminium silicate with a solution of potassium silicate 
and KOH in a tube at 100, and by heating muscovite in a solution of 
potassium silicate at 600 

Occurrence The potash feldspars are essential constituents of the 
igneous rocks granite, syenites, rhyohtes and trachytes and of some 
crystalline schists, and are accessory components of a number of other 
rocks They occur in most pegmatite dikes and as gangues in some ore 
veins, and m many contact metamorphosed rocks 

Localities* The potash feldspars are so widely spread that an enu- 
meration of their important occurrences is here impossible The best 
known localities of orthoclase are Cunnersdorf, Silesia, Drachenfels 
and Lake Laach, Rhenish Prussia (samdme), in the Ziller thai, Tyrol 
(adulana) , at St Gothard in the Alps (adularia) ; at Baveno, Italy, 
and at Mt Antcro, Chaffee Co , Col Microclme crystals arc well 
developed at Stnegau, Silesia; in the pegmatite dikes of southern Nor- 
way; and at Pike's Peak, Col (amcutomte). Anorthoclase occurs at 
Tyveholmen and other points in Norway and in the lava of Kilimand- 
jaro, Africa, and in that on Pantdlena, an island near Sicily. In 
North America pegmatites are abundant in" southeastern Canada, in 



416 DESCRIPTIVE MINERALOGY 

New England and in the Piedmont plateau area immediately east of 
the Appalachian Mts , and throughout this district all forms of the 
opaque potash feldspars are abundant Soda-potash feldspars ha\e 
been described from many places, but whether they j,ic soda orthoclase 
or anortholcase has rarely been determined 

All phases of the alkali feldspars occur as components of igneous 
and metamorphic rocks 

POTASH-BARIUM FELDSPARS 

The feldspars containing potassium and barium comprise an iso- 
morphous series with orthoclase and celsian as the two end members as 
follows 

Sp Or 

Ortioclase (Or) KAlSi 3 8 2 55 

Barium orthoclase Or^jCei OrjoCei 2 503-2 645 

Hyalophane Or-iCei-OrrC^i 2 725-2 818 

Cdsim (Ce) BaAl 2 (SiOi) 2 3 384 

The chemical composition of some of the barium feldspars are illus- 
trated by the analyses quoted below 

Si0 2 A1 2 3 BaO CaO MgO K 2 Na 2 O H a O Total 

I 51 68 21 85 16 38 10 09 . 100 oo 

II 52 67 21 12 15 05 46 04 7 82 2 14 58 99 88 

III. 53 53 23 33 7 30 3 23 n 71 . 99 xo 

IV. 54 15 29 60 i 26 i oo i 52 12 47 .. ioo oo 
I Theoretical for Or 2 Cei 

II Bmnenthal, Tyrol 

III Jakobsberg, Sweden 

IV Sjogrufran, Sweden. 

The minerals are isomorphous with orthoclase (with the possible 
exception of celsian, which may exhibit the triclmic habit and may more 
properly be isomorphous with microchmc), and their axial constants tire 
intermediate between those of orthoclase and celsian. The a\ial ratio 
for hyalophane is 6584.1 5512 01=90, |8 115 35', 7 = 00 Its 
cleavage angles are 90 Its crystals, as a rule, have the udularia habit. 
The Indices of refraction of the barium feldspars are: 

ft 7 

Barmm-orthoclase (OrioCei) i 5201 i 5240 i 5257 

Hyalophane (OnCei) i 5373 r 539S i 5416 

Hyalophane (Or 7 Ce 3 ) i 5419 i 5419 i 5469 

Celsian i 5837 i 5886 i 5940 



ANHYDROUS TRIMETASILICATES 417 

These feldspars are rare They ha\ e been found only m metamor- 
phosed dolomites in the Binnenthal, Valais, at the manganese mines at 
Jakobsberg and Sjogrufran, Sweden, and mtergrown with albite m a 
pegmatite at Blue Hill, Delaware Co , Penn 

SODA-LIME FELDSPARS 

Plagioclase is the general name given to the group of isomorphous 
feldspars of which albite and anorthite are the end members The 
albite and anorthite molecules are isomorphous in all proportions and 
the physical properties of the mixed crystals accord completely with 
their composition Certain mixtures are much more common than 
others These were given individual names before it was recognized 
that they were merely members of an isomorphous series and these 
names were later applied to mixtures of definite compositions The 
names and the compositions of the mixtures corresponding to them are 
given in the following table 

Si02 AbOs Na 2 CaO Sp Gr 

Albite NaAlSiaOsCAb) 68 7 19 5 n 8 2 605 

Ab(,Ani 1 64 9 22 i 10 o 30 

J 62 o 24 o 87 53 2 649 

I 

Ab]An t I 55 6 28 3 57 10 4 2 679 

AbjAni ] 

AbiAnj f 49 3 3 2 6 2 8 *5 3 2 708 

AbiAn fJ I 

AbiAn ( J 46 6 34 4 i 6 17 4 2 742 

Anorthite CdAl^SiCXjMAn) 43 2 36 7 20 i 2 765 



Qligodase 
Andenne 
Labrador ite 
Bytotvmte 



Nearly all plagioclases contain small traces of K20, MgO and Fc20s, 
but otherwise their composition is nearly in accord with that demanded 
by their symbols, so that if one constituent is known the others may 
be calculated Moreover, the accord between physical properties and 
composition is so close tlut from the former the latter may be de- 
termined 

Many oligoclascs, however, contain a large admktuie of the micro- 
clinc molecule so that they contain a notable quantity of KsO These 
are known as potadi-oligodc&e and are represented by the feldspar in a 
lock at Tyveholmen, Norway, the composition of which is as follows 

SiOa Al a On FcaOs CaO MgO K 2 Na 2 H 2 Total 
59 50 22,69 2 47 S S tr. 2 50 6 38 i 37 100 37 



418 DESCRIPTIVE MINERALOGY 

Some authors limit the name anorthodase to feldspars of this kind and 
designate the trichmc soda-potash feldspar as soda-microclme 

There is another group of soda-lime feldspars m which the anorthite 
molecule and an analogous sodic molecule (Na2Alo(SiCh)2) form iso- 
morphous mixtures The pure sodic molecule has not been found among 
minerals, but it has been prepared synthetically at temperatures above 
1248, under the name carnegieite Its sp gr = 2 513 and its refractive 
indices for yellow light are a=i 509, 7=i SH Although not known 
to exist independently it is believed to be present m the feldspar of 
Lmosa, near Turns, and possibly in other feldspars that have hitherto 
been described as plagioclases If future work establishes the fact that 
there is a distinct series of feldspars composed of isomorphous mixtures 
of anorthite and carnegieite it is proposed to name the group anemouute 
to distinguish it from the plagioclase group which comprises isomoiphous 
mixtures of anorthite and albite 

The Lmosa feldspar has properties nearly like those of the plagioclase 
AbiAm but its analysis yields the results m line I. The composition of 
is given in line II 



Si0 2 


A1 2 3 


CaO 


Na 2 


K 2 


Sp Gr 


53 26 


29 78 


10 76 


5 45 


75 


2 684 


55 67 


28 26 


10 34 


5 73 


oo 


2 679 



II _ 

THE 

All the plagioclases have a tnchmc habit, which is best expressed by 
the value of the angle between their cleavages, which are parallel to 
the planes ooi and oio The crystal constants of some of the common 
mixtures and the values of their cleavage angles are given in the table 
below. 



Albite a : 6 : <?- 6335 ' i = SS77 94 3' "6 29' %** Q' 86 24' 

Ohgoclase. -6321 i ' 55*4 93 4' n6 23' 90 5' 86 32' 

Andesme = 6357 - i 55*1 93 23' "6 29' 89 59' 86 14' 

Labradonte - 6377 : i : 5547 93 3*' "6 3' 9 55' 86 V 

Bytownite 

Anorthite - 6347 i = -55* 93 13' S 55' 9* ' 85 50' 

Crystals of the soda-rich plagioclases are rich m forms, but those of 
anorthite and the hme-nch members are much simpler Albite crystals 
are usually tabular parallel to oo P 06 (oio) and elongated parallel to 
c or a Others are elongated parallel to b (Fig. aai), Ohgoclase ib 



ANHYDROUS TRIMETASILICATES 



419 



more frequently columnar parallel to c, andesme tabular parallel to 
oo P So (oio) or oP(ooi), and labradorite and bytownite tabular parallel 
to oo P 06 (oio) Twins are e\en more common than among the potash 
feldspars Carlsbad (Fig 
222), Manebach and Ba- 
veno twins are not uncom- 
mon, but more frequent 
than these are the twins 
after two laws that are 
impossible in the feld- 
spars with a monoclinic 
habit The two most 
common twinning laws 
among the plagioclases are 
the albite and the pcncline 
laws 

In the albite law the twinning plane is oo P66 (oio) and the com- 
position plane the same (Fig 223) The twinning is usually repeated 
many times so that apparently homogeneous crystals may be built up 
of numerous lamellae parcel to oio Since the angle between oio and 





FK, 221 Albite Crystals with oo'p, no 
co P' ? no (/;/), oo P oo , oio (&), oP, oor (c) and 

;Py CO , Toi (l) 




Fie, 222 



Fro 222 Albite Twinned about oopcoj 100 Composition fate ool*oo,oro, 
Carlsbad law Compare Fig 316 

FIG 223. Albite Twinned about oo P So, oio Composition face the same Albite 
law Compare Fzg. 222 



ooi in all the plagioclascs is greater and less than 90, it must follow that 
the surface of then basal cleavages is not a plane, but that it consists of 
parallel strips of surfaces parallel to oio, and inclined to one another at 
angles alternately greater and less than 180. Therefore basal cleavages 



420 



DESCRIPTIVE MINERALOGY 




of the plagioclases very frequently exhibit parallel stnaUons when exam- 

ined in light reflected at the 
proper angles (Fig 224) 
It is this Ivunnmg uhich, 
repeated in submicioscopic 
lamelltie, is believed to pro- 
duce the monoclmic pseudo- 
syrnmctiy of orthoclase 
It will be noted that the 
twinning plane has the 
position of the plane of 

FIG 224 -Twmnmg StnaUons on Cleavage Piece hymmdiy in monodmiC 
of Ohgoclase (About natural bi/c ) crystals, and, consequently, 

twins about this plane have 

the same symmetry with reference to one anothci as amespomhng 
contiguous layers of mono- 
clmic crystals 

In the pencline law the 
twinned portions are super- 
posed The individuals are 
twinned about b as the twin- 
nmg axis, and are united about 

a plane nearly perpendicular 

^^/ \ i ^ 

to oo P 06 (oio), known as the 




Fio 225 Albile Twins with the Crystal 
* the Twinning Axis and llu- Khomlm Sci- 
u <> the Compos, turn F ; uc The form r is 

/l (43) Aniline law 
8 v * 



"rhombic section" (Fig 225) The position of this section vanes 
with the different plagioclases, but is always nearly perpendicular to oio 






Fio 226 



Flti. 2*7 



Fio 226 Position of " Rhombic Sections " m Albitc (*1) an<l Amwthitc (/*), 
FIG 227 Diagram of Crystal of Tnchnic Fciclbpar Kxhibilin Stnations Due to 
Polysynthetic Twinning According to the Albile and the Pcridmc Laws 

(Fig 226). As nearly all pencline twins arc elongated in the direction 
of the ft axis, and the twinning is repeated, lamellae arc produced, 



ANHYDROUS TRIMETASILICATES 421 

which, in sections perpendicular to oio, cross the albite lamellae at 
angles near 90 (Fig 227) It is the presence of the two kinds of 
twinning in microclme that gives it its peculiar grating structure m 
polarized light (see Fig 219) 

The plagioclases are light-colored, but pinkish and greenish shades 
are less common in them than in the potash feldspars Their streak is 
colorless They are usually translucent but in some cases are trans- 
parent Albite often exhibits a pearly luster and often a bluish shimmer 
Oligoclase when containing as little inclusions plates of hematite, glistens 
with a red shimmer and affords the finest sunstones The most bril- 
liantly colored plagioclases are some forms of labradonte, which, on 
cleavage surfaces, show a great display of yellow, green, red, purple and 
blue flashes m reflected light The cause of the play of colors is not 
known, but it is probably due to the presence of numerous very tuny 
parallel acicular inclusions 

The refractive indices of the plagioclases vary with their compositions. 
For yellow light the \alues for the specified mixtures are as follows 



5386 

5469 

556 

5634 

58os 

5884 

Before the blowpipe all the plagioclases fuse to a white or colorless 
glass, at the same time colonng the flame an intense yellow (albite), or a 
yellowish red (anorthite) Albite fuses at a lower temperature than 
anorthite The temperatures at which synthetically prepared plagio- 
clases melt completely are as follows 



Albite (Ab l0 oAn ) i 5290 i 5333 

Oligoclase (Ab?sAn22) i 5389 i 5431 

Andesme (Ab&oAn4o) i 549 i 553 

Labradonte (AbisAn,^) i 5545 i 5589 

Bytowmte (AbaoAngo) i 5691 i 5760 

Anorthite (AbgAnoi) i 5752 i 5833 



Anorthite i>55o 

1,521 AbsAni 1,362 

i,49 Ab4Ani 1,334 

1,450 AbsAni, 1,265 

Albite 1,100 est 

Albite is unattacked by HCi, but anorthite is decomposed by this reagent 
with the separation of gelatinous or pulverulent silica The intermediate 
plagioclases are more or less easily decomposed as they contain more or 
less of the anorthite molecule 

The plagioclases are distinguished from the feldspars possessing the 



422 DESCRIPTIVE MINERALOGY 

monochmc habit by the twinning stnations on their basal cleavages, 
and from the potash feldspars of both monochmc and triclimc habits by 
the color imparted to the blowpipe flame The characteristics of the 
plagioclases best distinguishing them from one another are their specific 
gravities and their optical properties 

The plagioclases weather to kaolin and mica (paragonilc) mixed 
with quartz and calcite in the more basic varieties, and to zeolites (see 
p 45) In rock masses the more basic varieties alter to epidote, m 
some instances into scapohte (p 423), and very commonly into the mix- 
ture known as saussunte, which is an aggregate containing /oisite or 
garnet as its most important component 

Syntheses Crystals of plagioclase have been nude by processes 
analogous to those employed in making oithoclase crystals For exam- 
ple, albite crystals have been produced by fusing SiOy and Al 2 0;j with 
sodium wolframate, and by heating precipitated aluminium silicate with 
a solution of sodium silicate m a platinum tube to 500 Anorthite 
crystals have been made by long heating of a mixture of SiOj, AbQs 
and CaCOs m the proper proportions, and by fusing vcsuvianilc and 
garnet 

Occurrence Albite occurs m vein masses in certain crystalline schists 
but is much less common as a primary rock constituent than the other 
plagioclases It is, however, frequently found as a secondary product 
resulting from the changes produced m other plagiochuses by mclamor- 
phic processes, thus it is common in many crystalline schists Oligo- 
clase and andesme occur m granites and the other 
/s^=~v more siliceous igneous rocks and Ubradorite, by- 

/ >> towmte and anorthite m the more basic rocks 

Anorthite has also been found m meteorites 

Localities The localities at which crystals of 
the plagioclases are found are too numerous to be 
mentioned here Especially line crystals of albite 
occur at Roc-Tourn6 in the French Alps, m 
DaupmnS, France, at Amelia Court House, Va , 
FIG 2 28 Potash- at Middletown, Conn, and at Chesterfield m 
Oiigoclase Crystal Massachusetts Excellent crystals of oligoclase 
Forms u m and c occur at Arendal and at other places in Norway, and 

?R ?3oV(y) at McComb and Fme > m St Lawrence Co., N. Y. 

Potash-ohgoclase occurs m certain igneous rocks at 

Tyveholmen and elsewhere in Norway and in the lava of Kihmamljaro, 

Africa. Its habit is prismatic (Fig 228) Crystals of andesme are 

found at Bodenmais, m Bavaria, Arcuentu, in Sardinia, and at Sanford, 




ANHYDROUS TRIMETASILICATES 423 

in Maine Labradonte crystals occur at Visegrad, Hungary, and at 
Mt Aetna, Italy, and beautiful cleavage pieces come from Labrador, 
where it forms one of the constituents of a coarse-grained igneous rock 
Anorthite crystals occur at Volpersdorf, in Silesia, in the Aranya Mt, 
Siebenburgen, Hungary, at Pesmeda, Tyrol, in the inclusions in the 
lavas at Vesuvius, Italy, m the lava on the Island of Unjake, Japan, 
and at Phippsburg, in Maine. 

Uses Albite from the pegmatite veins of southeastern Pennsylvania 
and northeastern Maryland is mined for use in pottery manufacture 

SCAPOLITE GROUP 
(Na4Al 2 (AlCl)(Si 3 8 )a-HCd4Ai fi (A10)(Si0 4 ),) 

The scapohtes comprise a series of isomorphous compounds of which 
the two end members are manaltte, Na4Al2(AlCl)(Si30s),j and mewnite> 
Ca4Alf,(A10)(Si04)(), Between these two are many intermediate com- 
pounds known under the collective name miz&omte Their composition 
is represented in terms of the manahte and meionite molecules, thus, 



The theoretical compositions of the two end members of the series 
and of several intermediate members, and the actual compositions of 
four specimens of natural crystals are given below 





Si0 2 


AlaOs CaO 


Na 2 O 


Cl 


Total 


Theoretical, Ma . 


63 95 


18 12 




< 


14 


69 


4 


19 


100 


95 


Theoretical, MasMe 


57 85 


22 35 


6 


53 


10 


87 


3 


10 


IOO 


70 


Theoretical, MagMe . 


55 85 


23 73 


8 


67 


9 


62 


2 


75 


100 


62 


Theoretical, MaMe 


Si 9 


26 47 


12 


90 


7 


IS 


2 


04 


IOO 


46 


Theoretical, MaMe 2 . 


48 03 


29 16 


17 04 


4 


76 


I 


35 


IOO 


34 


Theoretical, MaMes 


46 10 


30 48 


19 10 


3 


54 


I 


01 


IOO 


23 


Theoretical, Me 


40 45 


3438 


25* 


i? 










IOO 


oo 


Si02 AlaOs 


CaO 


Na 2 


K 2 


H 2 Cl 


Total 


I 61 40 19 63 


4 xo 


? 


? 








4 


00 






II 54 86 22 45 


9 09 


8 36 


i 13 




86 




2 


41 


IOO 


45 


III 49 40 30 02 


15 62 


3 " 


79 




64 






13 


IOO 


03 


IV 41 80 30 40 


19 oo 


2 Si 


86 




3 i? 


* 






98 


66 



I. Manahte, Piaiwra, Italy 

II Ripomte, Ripon, Quebec Contains ako 80% SOg, 49 Fe/>3 and a trace 
of MgO 

III Werncntc, Rossie, N Y Contains also 10% 80s and 32 FeO. 

IV Meionite, Mt, Vesuvius Contains also 46 MgO and 46% undecomposed 

material 

*Volatile 



424 



DESCRIPTIVE MINERALOGY 



All the members crystallize in the pyramidal hemihedral division of 
the tetragonal system (tetragonal bipyramiclal class) in fairly simple 
columnar crystals with an axial ratio i . 442 for manahte and i 4393 
for meionite The principal forms are oP(ooi), oo P oo (ioo), oo P( T 10), 



oop 2 (2io), P(III), Poo (101) and 



22 <>) The angle 





in A ill =43 45' The habit of the crystals is always tolumnai , with 
oopoo(ioo) predominating in the prismatic zone, and also ooP(no) 

prominent The Litter form 
predominates only m miz/on- 
ites The scapolites occur also 
in crystal grams embedded in 
limestones, in columnar and 
fibrous aggregates and in struc- 
tureless masses 

All the scupohtes have a 
glassy lustei, which approaches 



pearly They aie transparent 
translucent, colorless or 



or 



FIG 229 Scapohtc Crystals with oP, 
1 10 (w), oo Poo, ioo (a), P, ii (r), and 

311 (s) white, giay, greenish, bluish or 

reddish and have a white 
streak Their cleavage is nearly perfect paiallcl to oo poo (roo) and 
imperfect parallel to ooP(no) Then fracture is uneven 01 con- 
choidal They are brittle, have a hardness of 5- 6 and <i density of 
2 54 fpr manahte and 2 76 for meiomte, The refractive indices 
naturally vary with the proportions of the two molecules present. 
For the two end members of the group the indices for yellow 
light are marialite, w= 1.5463, 6=15395, meiomte, o>=r.5897, 

=15564- 

Before the blowpipe all members swell and fuse to a white glass In 
hydrochloric acid, mixtures between Ma and MagMe arc insoluble, those 
between Ma2Me and MaMe2 are partially soluble and those between 
MaMe2 and Me are nearly completely soluble. 

All members of the senes are distinguished by their crystallization 
and cleavage and all except pure meionite are characterised by the 
chlorine reaction They are distinguished readily from the feldspars 
by their fusibility with swelling, 

Manahte and meionite are rare The common scapolites are the 
mizzonites of which dipyr and wernerite are the nontrunspurent vari- 
eties The former includes varieties occurring in elongated prisms con- 
taining between 54 per cent and 57 per cent SiOs, i.c., MaaMe to MagMe, 



ANHYDROUS TRIMETASILICATES 425 

and the latter embraces varieties containing between 54 per cent and 46 
per cent SiCfe, or Ma2Me to MaMea 

Occurrence The scapohtes occur in crystalline schists, crystalline 
limestones and also m limestones included m volcanic lavas (meiomte), 
and on the contacts of igneous masses (wernente) They are found also 
m igneous rocks as the result of alteration of the feldspars, especially 
when these rocks are intrusive m limestones, and also as an alteration 
product of garnets In a few places they are associated with magnetite 
and apatite in veins of iron ores In most cases they appear to have 
been derived from feldspars by the action of metamorphic processes 
On the other hand, scapohte changes to albite, epidote, bio tit e, musco- 
vite and to a mixture of minerals 

Localities Meiomte crystals occur in the fragments enclosed in the 
lavas of the Lake Laach region, Prussia, and of Monte Somma, the 
precursor of Vesuvius, Italy Mizzonite is associated with meiomte 
at Monte Somma Dipyr occurs m clayey limestones m the Pyr- 
ennees, wernente at Arendal and Bamle, Norway, at Malsjo, m 
Sweden, at Diana, Lewis Co , and at Gouverneur and Pierrepont, 
St Lawrence Co , N Y , at Canaan, Conn , at Bolton, Mass , and 
manahte at Ripon, Quebec, and at Pianura, near Naples, Italy 



CHAPTER XIX 

THE SILICATES Continued 

THE ANHYDROUS POLYSILICATES 

UNDER the polysihcales are grouped all the minerals that cannot 
easily be assigned to the orthosilicates, the metasihcates or the tri- 
metasilicates They are usually very complex in composition and are 
commonly regarded as isomorphous mixtures or solid solutions of silicate 
molecules of various types* 

THE BRITTLE MICAS 

The brittle micas are so called because, while they possess a very 
marked cleavage which rivals that of the true micas in its pcifection, 
their cleavage foliae are brittle, and not elastic as arc the mica fohae 

The group consists of four minerals of which throe are apparently 
mixtures of the molecules H2CaMg4(SiOi)s and HaCaMgAi^O^, and 
the fourth is approximately H2(Fe MgJAbSiO? The drst three are 
known as xantkopkylhte, brandtstte and chntomte and the fourth as 
ddoritoid Of these the last two are the most important Chloritoid 
is believed to be a basic orthosilicate, but, because of the similarity of its 
properties to those of the brittle micas, it is thought best to discuss it 
in the same group with them 

All members of the group crystallize in the monocimic system with 
an hexagonal habit. 



Clintomte (H (Mg-Ca 

Clmtomte, or seybertite, may be regarded as a mktuie of the mole- 
cules H2CaMg4(Si04)3 and HaCaMgAleOia in the proportion 4 : 5, 
which requires the percentage composition shown in line I below. The 
analysis of a specimen of the mineral from Orange Co., N. Y., is given in 
line II 



Si0 2 A1 2 3 FeaOs FeO MgO CaO H 2 F Total 

11909 4097 2228 13.36 430 .... 100.00 

II 19 19 39 73 61 i 88 21 09 13 n 4,85 1,26 101.72 

426 




ANHYDROUS POLYSILICATES 427 

Well developed crystals are so rare that their axial ratio has not been 
satisfactorily established The best crystals appear as long, thick, six- 
sided plates with a well developed basal plane and several pyramids and 
domes with rounded edges If the axial ratio is assumed to be the 
same as that for biotite the principal forms are oP(ooi), -f P ob (027), 
P * (056), fP & (052), -iP(ii4), -?P(337), and -2P( 2 2i) Many 
r A the crystals are superposed twins, like 
those of muscovite (Fig 230) 

The mineral is reddish or brown, and 

transparent or translucent It has a glassy 

luster and a white streak Pressure and FIG 230 -Clmtomte Twinned 

r t j j , , According to the Mica Law 

percussion figures are easily produced on the Formg ^ m ( ^ _, p> 

cleavage plates, and in nature parting often 337 ^ and ;P 5* , 012 (u) 
takes place along these directions, yielding 

fragments with rectangular edges The hardness of clintomte is 4-5 
and its density 3 i Its refractive indices for yellow light are = i 646, 
0=1657, 7=1658 

Before the blowpipe clintomte becomes white and opaque but does 
not fuse In the closed tube it gives off water It is completely decom- 
posed by hydrochloric acid 

It is distinguished from most other minerals by its micaceous cleav- 
age, and from the true micas by its brittleness and solubility in hydro- 
chloric acid 

Clintomte occurs in a coarse, serpentimzed limestone at Amity, 
Orange Co, N Y 

Chlontoid (H 2 (Fe-Mg)Al 2 Si07) 

Chlontoid differs from the other brittle micas in being essentially a 
ferrous compound Its composition approaches the formula given 
above, though the analyses of many specimens depart widely from this. 



Si0 2 AlsOs FeO MgO H 2 Total 

I 23 72 40 71 28 46 7 ii ioo oo 

II 25 50 38 13 23 58 5 19 6 90 99.30 

I Theoretical for HjFeAl 2 Si0 7 
II Specimen from chlorite schists, St Marcel, Italy 

The mineral is believed lo be monochmc m crystallization because of 
the similarity of its crystals to those of biotite It often occurs in six- 
sided plates, but more frequently m lenticular or spindle-shaped grams 
and sheaf-like and ball-like aggregates of plates and grains and in foliated 
masses Twins like those of biotite are also fairly common. 



428 DESCRIPTIVE MINERALOGY 

The mineral is dark green or black, and translucent It is strongly 
pleochroic in olive green, blue and yellowish green tints It has a 
glassy or pearly luster on its cleavage faces and a waxy luster on frac- 
ture surfaces Its hardness is 6-7 and density 3 4-3 6 Its refracti\e 
index is i 741 

Before the blowpipe chloritoid exfoliates on the edges and fuses with 
difficulty to a black magnetic mass In the closed tube it gi\ cs off water 
It is unattacked by hydrochloric acid, but when in Jmc powder is com- 
pletely decomposed by sulphuric acid Some forms of ott relit e are sol- 
uble m strong nitric and hydrochloric acids, with the separation of 
gelatinous silica 

Masonite is a dark grayish variety from Nalick, R I 

Qttreltte contains a little manganese and has a slightly chfTcicnt 
formula from chloritoid Its composition may be best represented by 
Ha(Fe MnjAJaSfcOo Itssp gr=33 

The chlontoids appear to be fairly stable, as their only alteration 
products thus far noted are the chlorites and the micas and otti elite 

Occurrence All varieties of chloritoid are found principally m fine- 
grained schists where they are believed to be the result of regional and 
contact metamorphism 

Localities The most noted occurrences of chloritoid are Pregattun, 
Tyrol, St Marcel, Italy, Ottrez, Belgium; Natick, R, I , and Augusta 
and Patnck Counties, Va, 

CHLORITE GROUP 

The chlorite group is so named because its principal members are 
green. The group comprises a number of platy hyduws magnesium, 
aluminium silicates that appear to be isomorphous mixtures of mole- 
cules that are approximately BLi(Mg Fe^AlgSiOu and H,| (Mg- FcXiSisOu, 
the former of which is known as the amesite molecule (designated At), 
and the latter as the serpentine molecule (indicated by Sp). The ser- 
pentine molecule is represented in the platy form of serpentine known us 
anhgonte, which may be regarded as one of the end members of the 
series The independent e\istence of the arnesite molct ult 1 is doubtful 
The mixture of these two molecules gives rise to the orthot ///orz/rs, which 
constitute the principal of the two subgroups of the chlorites. The 
other subgroup is known as the group of the leptocUmfa These con- 
sist of one or both of the two molecules mentioned above and others that 
may be regarded as derived from them Their composition is too com- 
plex to be represented by any simple formula 



ANHYDROUS POLYSILICATES 429 

ORTHOCHLOR1TES 

The orthochlontes comprise the minerals 

Si0 2 AI 2 3 FeO MgO H 2 

Coru'ndoph^hleSpA.U-Sp3A.t7 SpAU =26 i 29 3 31 8 12 8 

Prochlonte Sp3At7~Sp 2 At3 SpAt 2 =25 5 21 6 26 6 14 9 n 4 

Chnochlore Sp 2 Ata-SpAt Sp 2 Ats=3o 03 22 o 34 8 12 9 

Pennimte SpAt -SpaAt 2 SpsAt2=34 7 14 6 37 7 13 o 

Analyses of typical specimens are as follows 

Si0 2 A1 2 O 3 Fe 2 O* FeO MgO CaO H 2 Total 
I Corundophihte 24 77 25 52 15 19 21 88 n 98 99 34 

II Prochlonte 26 02 20 16 i 07 28 08 15 50 44 9 65 100 92 

III Chnochlore 29 87 14 48 5 52 i 93 33 06 13 60 100 19* 

IV Pennimte 33 71 12 SS 2 74 3 4 34 7 66 12 27 100 03 

I Chester, Mass 

II Zillerthal, Tyrol 

III West Chester, Pa 

IV Zermatt, Switzerland 

* Contains also NiO= 17, Cr2O3=r 56. 

The orthochlontes crystallize in tabular and pyramidal crystals that 
are usually repeated twins so that their true nature is difficult to decipher 
The simpler crystals have a monoclmic habit, but the twins are usually 
hexagonal or rhombohedral in habit Then crystallization is believed 
to be monoclmic, with the axial ratio 5774 .1:2 2772 and =89 40', 
The most common forms appearing on them are oP(oor) ; Pob(oii), 
?P(22 S ), ]P(Ti2), JP&(043), -AP (40.11), oop6b(i OI ) and 
6P^(26i) (Fig 231) Twins are very common The two most com- 
mon twinning laws are the mica and the pennme laws In the former 
the twinning plane is perpendicular to oP(ooi) and in the zone with 
oP(ooi) and aP(ii2) (Fig 232, compare Fig 193) The two parts 
are levolved 60 with respect to one another In the pcnnine law 
oP(ooi) is the twinning plane and the composition face (Fig 233) 
Twins following the first law have their twinned parts either side by 
side (Fig 234), or superposed (Fig. 232^ Those following the pennine 
law have their parts superposed The twinning is often repeated so 
that complicated trillings and sixhngs are produced 

Chnochlore crystals are tabular with hexagonal outlines but a mono- 
clime habit (Fig 231), and penmmte is in thick tabular crystals with a 



430 



DESCRIPTIVE MINERALOGY 



trigonal outline and a rhombohedral habit, or in slender prismatic ones 
resembling steep rhombohedrons (Fig 235) Its characteristic twins 
are according to the penmne law (Fig 236) Prochlonte and corun- 
dophilite are found in six-sided plates without well developed crystal 
forms. 




FIG 231 FIG 232 FIG 233 

FIG. 231 Clmochlore Crystal with oP, ooi (c), Pcb, oio (?>), 4P3, 401 (f), 

and -^Ps, 132 W 

FIG 232 Clmochlore Twinned According to Mica Law, in which the Twinning 

Plane is Perpendicular to oP(ooi) and in the Zone with oP(ooi) and -lP(ii2) 

Forms oP, ooi (c), JP oo , 31 o 30 (/) , -6PJ , 261 (i>) and ?2P> , 9 27 17 (<*>) 

FIG. 233 Clmochlore with Same Forms as in Fig 232 Twinned about oP(ooi) as 

Twinning and Composition Face, Pennine law. 






FIG 234 



FIG 235 



FIG 236. 



234 Clmochlore Tnllmg Twinned According to Mica Law, but with Individuals 
Side by Side with oP(ooi) common and Irregular Compoulion Faces* =$?, 
(225) and y- |P 55 (205) 

2 35 Pennmite Crystal with oP, ooi (c) and a Form Resembling 3!*, 3031 (w). 
FIG 236 Pennmite Crystal Twinned about oP(ooi), Pennine Law 



The orthochlorites have a glassy luster with a slightly pearly luster 
on the basal plane. They are usually some shade of green, blackibh and 
bluish green being the most common shades. At a few localities white 
or yellow varieties are found. Varieties containing chromium are often 



ANHYDROUS POLYSILICATES 431 

rose-colored or violet The streak of all varieties is white or light 
green All are strongly pleochroic in shades of green m gieen vari- 
eties, yellow and brown in brown varieties, and violet and carmine in 
rose varieties Their cleavage is distinct parallel to the base (ooi), 
yielding lamellae that are flexible and slightly elastic Percussion and 
pressure figures, with rays in the same relative positions as m the 
micas, occur naturally and often a parting takes place along their 
planes yielding triangular plates The hardness of all orthochlontes 
is below 3 and their density is 2.5-3. For the different varieties these 
properties are. 

H Sp Gr 

Prochlonte 1-2 2 78-2 96 

Clmochlore 2-2 5 2 65-2 78 

Pennmite 2-2 5 2 6 -2 85 

Corundophihte 25 29 

The refractive indices for yellow light are* in penmmte, *=r 575, in 
chnochlore, a i 585, 0=i 585, 7=1.596, m prochlonte, #=i 58+ and 
in corundophihte, =1 583 

Before the blowpipe the orthochlontes exfoliate and fuse with diffi- 
culty. Some varieties whiten The varieties rich in iron fuse more 
readily than those m which there is little iron in some instances to 
a black glass In the closed tube all yield water when strongly heated 
Hydrochloric acid attacks all varieties with difficulty after fusion with 
more ease Sulphunc acid completely decomposes them 

Synthesis Chlontes have been produced artificially by the action 
of alkaline solutions on pyroxenes. 

Occurrences The orthochlontes are alteration products of various 
silicates They occur as essential constituents m crystalline schists 
(chlorite schists), and as the alteration products of silicates in igneous 
rocks, in which case the latter assume a green color The orthochlontes 
also form pseudomorphs after garnet, biotite, augite, hornblende, etc , 
and sometimes they occur filling little veins cutting through altered 
rocks Corundophihte is frequently associated with the mineral 
corundum 

Localities The localities at which the orthochlorites occur are so 
numerous that even all of the most important cannot be mentioned here. 
In the United States corundophihte occurs at Chester, Mass., and 
Asheville, N C , pyrochlorite at Foundryrun, Georgetown, D C , and 
at Batesville, Va , pennmite at Magnet Co^/c, Arkansas, and chnochlore 
at West Chester, Penn 



432 DEBCBIPT1\E MINERALOGY 

LEPTOCHLORITES 

The nameleptochlonte is usually given to the chlontes that occur in 
fine scales and fibers They are very complex in composition Because 
they do not occur ui distinct crystals the.r crystallization ,s not ceitamly 



e leptochlorites are hke the orthochlontes in general appearance, 
and in origin They are, however, completely soluble m hydrochloric 
acid with the separation of gelatinous silica 

Of this group thuringite and ddesvte are the best known The former 
1S in very fine dark green and pleochroic scales It fuses to a black mag- 
netic bead It forms pseudomorphs after garnet at the Spurr Mt iron 
mine at Spurr, Mich Delessite is usually green, but w in lare cases 
nmk' It usually occurs in bundles of fibers that are strongly pleochro.c 
The green varieties, viewed across the fibers are dark peon Viewed 
along their axes they are yellow This chlorite is a common alteration 
product of pyroxene and amphiboles, and it frequently occuih as he 
filling of amygdules in basic volcanic rocks The minoul when heated 
becomes brown or black and finally fuses with dfficulty to a black mag- 

neticbead . . . ., 

Analyses of typical specimens of the two minerals are given m the 

following table 

Si0 2 Ai 2 03Fe 2 3 FeO CaO MgO H 2 Total 
Thunngite, Spurr, 

Mich ' 22 35 2 S 14 34 39 - 6 4i 25 99*S4 

Delessite, Dum- 

barton, Scot- 

land , 32 oo 17 33 i 19 "-4S I 57 20.4^ IS 45 * 4i 



Vesuvianite 

Vesuvianite is a common metamorphic mineral in limestones. 
It is extremely complex m composition, apparently consisting of 
isomorphous mixtures of the two compounds CaAlaAl(OII'F)(Si04)5 
and Ca 2 Al(OH)Si 2 07 Its composition may perhaps be better rep- 
resented by the general formula R'4Al 2 Ca 7 Sio0 2 4, in which R/4 may be 
Ca 2 ,(A10H) 2 , (A10 2 H) 4 or H 4 Four analyses, which emphasis the 
great variations m composition shown by crystals from different localities 
are quoted below* 



ANHYDROUS POLYSILICATES 



433 





Si0 2 


AbOs 


Fea0 3 FeO 


CaO 


MgO 


MnO 


K 2 


I 


36 08 


9 35 


7 


61 






29 09 


i 90 


12 


49 


28 


II 


37 ii 


IQ 30 


3 


3 1 






36 24 


3 89 








III 


36 41 


i7 35 




i 


86 




33 21 


i 38 


I 


75 


5 


IV 


36 55 


18 89 




74 




74 


35 97 


2 33 









NaaO F H 2 at 100 H 2 0+ 



Less 0=F Total 



I 55 
II 

III 44 
IV 



58 
36 
13 



24 
58 



3 32 


100 67 






06 


100 49 


24 


100 25 


3 5i 


100 23 


IS 


100 08 


3 42 


100 26 


05 


IOO 21 



I Garnet colored masses and crystals form Pajsberg, Sweden 
II Finely crystallized material from Italian Mt , Gunnison Co , Colo 

III From Franklin Furnace, New Jersey Contains also ZnO=i 74, 

i 48, and a trace of PbO 

IV Cahformte Fresno Co , Cal Also 91 per cent CO. 



CuO= 



Vesuviamte occurs both massive and crystallized Its crystals are 
m the tetragonal system (ditetragonal bipyrarmdal class), with an axial 
ratio of about i 5375 This 
vanes with the composition 
and is, therefore, different m 
specimens from different lo- 
calities The crystals are 
usually thick columnar m 
habit, but some ciystals are 
pyramidal and otheis acicular. 

The columnar crystals usually 237suviamte Crystdlb Wlt IIO 

(m]j oopoo,ioo (a), l\ in (p) and oP, 
oox (c) 





In 



contain ooP(iro) and oPoo 

(100) m the prismatic zone, 

and oP(ooi), P(in), and 

often POO(IOI), 3P(33i), oP 2 (2io), and 3^3(311) (F 237) 

all about 60 forms have been observed on them The angle 

= 5o 39' 

The mineral is glassy in luster and yellowish, greenish or brownish, 
rarely blue or pmk It is transparent or translucent. A bright green, 
or gray and green, translucent, massive variety from points in California 
is used as a gem under the name cah/ornite. The streak of all varieties 
is white The cleavage of the mineral is indistinct parallel to oo P(no) 
and oo Poo (100) and its fracture conchoidal. Its hardness is 6-7 and 
density 3 35-3.45. Its refractive indices foi yellow light are w= 1.705, 
= i 701 



434 DESCRIPTIVE MINERALOGY 

Before the blowpipe vesuviamte melts to a swollen brown 01 green 
glass It is decomposed with difficulty by cicids, but after being strongly 
heated it dissolves with the separation of gelatinous silica The min- 
eral powder reacts alkaline 

The mineral is characterized by its form when in crystals and by its 
easy fusibility 

The recognized varieties that are used as gems are 

Cdtformte, a white, green or gray and green variety in finely gran- 
masses, resembling jade 

Cypnne, a blue variety containing copper 

Its principal alteration products are mica, chlorite and steatite, 
and other minerals are also known to be foimed from it by weathering 

Occurrence Vesuviamte is preeminently a contact mineral It 
occurs in limestone metamorphosed by granite and othei igneous rocks, 
and also in crystalline schists It is found also as well developed crys- 
tals on the walls of veins containing quart/, calcitc, gurnet and ore 
minerals 

Localities Good crystals are common at a number of places where 
limestones are in contact with igneous rocks, notably at Piitsch, and in 
the Monzom Mts , m Tyrol, at Zermatt and at othei points m Switz- 
erland, at Vesuvius, in the Alathal, and the Albanian Mts,, m Italy, 
and at many places m Norway and Sweden In North America good 
crystals occur at Sandford, Phippsburg and other places in western 
Maine, near Amity, N Y , and at Templeton, Quebec, and a fine- 
grained, massive variety occurs in Inyo and Tulaie Counties, in Cali- 
fornia Californite is best known from Indian Cieck, Siskiyou Co , and 
from a point 35 miles east of Sclma, m Fresno Co , California Other ' 
localities are at Big Bar Station, Butte Co , and Kxctcr, in Tulare Co., 
m the same State 

Production The quantity of californite used as a gem stone in 
1909 was about 3,000 Ib , valued at $18,000 In 1912, however, only 
$275 worth was used 



Tourmaline (RoAl^ (B OH* F) a 
R=H, Al, Mg, Fe, Al, Cr, Fe, K, Na 

Tourmaline is of great scientific interest because of its complex crys- 
tallization, its handsome crystals and the phywcal properties which it 
exhibits so beautifully. Moreover, it furnishes gems of many colors, 
which, because of their brilliancy, are greatly admired by many persons 
The mineral appears to be a derivative of the alumino-borosilicic acid 



ANHYDROUS POLYSILICATES 435 



in which the hydrogen may be replaced by Al, 
by Cr, by Mg and Fe" or by Li or Na, giving rise to four groups of com- 
pounds between which are many gradations Moreover, in most speci- 
mens a portion of the hydroxyl is replaced by fluorine In other words, 
the mineral is an isomorphous mixture of several substances that are 
derivatives of the alummo-borosihcic acid mentioned The four groups 
of tourmalines that are clearly distinguishable are 

1 Alkah tourmalines, which are colorless, red or green, and trans- 
parent 

2 Iron tourmalines, which are usually dark blue or black and trans- 
lucent 

3 Magnesium tourmalines, which are yellowish brown, or brownish 
and translucent 

4 Chrome tourmalines, which are dark green, black and translucent, 
or colorless and transparent 

Typical analyses of these four varieties follow 

I II III IV 

SiO 2 38 07 34 99 37 39 3^ 56 

9 99 9 63 IO 73 8 90 

42 24 33 96 27 89 32 58 



FeO 26 14 23 64 

MnO 35 .06 

CaO 56 15 

MgO 07 i 01 

NaaO 2 18 2 or 

&20 44 34 

LiaO i 59 tr 

HfeO 4 26 3 62 

F 28 

Ti0 2 

Total . 100 29 100 oo 100 42 99 70 

I Rose-colored (rubellite), from Rumford, Maine 
II Black, from Auburn, Maine 

III Brown, from Gouverneur, N Y. The A1A includes ,10 of Fe 2 8 . 

IV Green, from Etchison, Montgomery Co , Md Contains also 79 FcjOj, 05 

NiO and 




The varieties recognized by distinct names are (i) ordinary, black and 
brown, (2) rubellite, pink or red, (3) indicolite, blue or bluish black, (4) 



436 



DESCRIPTIVE MINERALOGY 



Brazilian sapphire, blue and transparent, (5) Brazilian cm&ald, or 
Brazilian chrysolite, green and transparent, (6) peridot of Ceylon, honey- 
yellow and transparent and (7) acfaoite, colorless and transparent 

Tourmaline forms handsome crystals that are frequently character- 
ized by possessing a triangular cioss-section They ciystalh/c in the 
rhombohedral division of the hexagonal system and aie hemimorphic 
(ditrigonal pyramidal class), with an axial ratio of i 4474 The crys- 
tals are usually prismatic or columnar in habit, and ore teimmated by 




FIG 238 



FIG 239 



00